Archive for the ‘Prime Factorization’ Category

Swatching a Prime Factorization Blanket!

Tuesday, December 4th, 2012

I’m excited! My little brother Robert’s wife is having a baby. Since Robert is even more mathematically minded than I am, if that’s possible, I definitely think his baby needs a prime factorization blanket. I had to laugh, though, because when I told him this instead of expressing gratitude, he said, “Okay, but we’ll have to talk about the representation of 0 and 1.” I remembered that a long time ago when I showed him my prime factorization sweater, he told me that he thought the rows should start with 0, 10, 20, and so on.

Now, I don’t want to include 0. Primes and composite numbers are properties of the natural numbers. But then I had a brilliant idea: Why not leave a hole for zero? Now to figure out how to work that in.

Mind you, I wasn’t prepared to make another grid like my original sweater. I wanted to do something different, and I didn’t want to have to have several colors dangling as I knitted each row. I also didn’t want to use stripes like my prime factorization scarf or the prime factorization cardigan I’m working on. To make a wide enough blanket, that would take far too much yarn. That’s what gave me the idea of using entrelac, that and a brand new book I’d had sitting in my house for a few months called EntrĂ©e to Entrelac, by Gwen Bortner.

I ended up making three swatches. Now, there are things I don’t like about all three swatches, but I think I learned enough to decide how to make the blanket. The only decision left is what colors to use. I don’t think they know the gender yet, so I probably won’t use blue or pink for 2 or 3. (Though maybe if I used blue for 2 and pink for 3 it would work for either gender — but I’ll probably go with yellow and green if they don’t know in the next few days.)

I planned to use Cotton Classic, the same yarn I used for my original sweater, because I can use the leftover colors from that sweater for a lot of the larger value factors, so I won’t have to buy that much additional yarn. On they had a sale on Cotton Classic, but no off-white, so I’ll go with a white background, which is nice for a baby blanket (though it won’t stay clean — but that’s their problem, teehee). Of course, that’s what I thought, but the total (for some additional colors) was a lot more than I’d usually spend on a baby gift, but I’m going to have so much fun with it, it’s totally worth it.

I decided the easiest way to break a block into factors would be to have 12 stitches and 24 rows. (Entrelac normally has twice as many rows as stitches.) This would divide naturally for 2, 3, 4, or 6 factors, and I can work something out for 5 factors.

The first swatch I made half that size because I didn’t want to do an enormous swatch. I made it base 4. I used white triangles on the outside and a hole for zero. Before I even show the swatch, I’ll say the things I didn’t like:

The hole didn’t work out very well. It wasn’t going to be very stable. I didn’t like the way the border triangles came out, and I didn’t like using white in between factors — too many yarn ends. It all curled way too much. The colors didn’t make me happy, and I knew I wasn’t happy with it. Here’s that first try:

Okay, I decided to get rid of the triangles and just use white rectangles on the outside and just leave one corner missing for zero. I also decided to make the swatch full size with 24 rows, not 12 like the previous. And I decided to try the wool/acrylic blend I used for my prime factorization scarf. Here’s how the second swatch came out:

What I did like about this swatch was using a ridge instead of a band of white between factors. Much easier and will involve less ends to sew in. The yarn was softer, but it would make a much bigger blanket, and I thought I’d rather use the cotton after all. I decided the outside white rectangles were completely unnecessary. The biggest thing I didn’t like was that the edges were curling way too much.

So the kind of obvious solution for curling edges? Use garter stitch instead of stockinette. A bonus is that then it will be easy to count ridges to divide up a block. I’m very happy with everything in the last swatch (this time base 3) except the particular choice of colors. (I hate that orange! And the green shade didn’t turn out very lovable.) Instead of a ridge where there are factors, I’ve got the lack of a ridge. I think this might work!

I should mention that the actual blanket will be rows of 10, but I wanted to work out the overall scheme with less.

The most lovely thing about doing the blanket in entrelac instead of intarsia, like I did the original sweater, is that I can knit one number at a time, and I can do it in order! So I don’t even have to plan it all out ahead of time, I can just jump in and knit! So — I will be knitting the rectangle for 1, and once I finish that, I will have to make a decision about the color to use for 2. Will I find out the baby’s gender before I begin? Either way, it’s going to be a unique and beautiful blanket, if I do say so myself.

My posts on Mathematical Knitting and related topics are now gathered at Sonderknitting.

Mathematical Knitting — Blessing Blanket

Saturday, November 17th, 2012

Alyssa Karise is here! And her blanket is ready to send! Here’s the finished blanket. It’s actually a rectangle, but I wanted the message to be in the picture, reading from the top to bottom, left to right, so the perspective warps it a little.

I used Base 5 math to code a message into the blanket, which I explained when I started. But now I can show you how it worked out.

You can see in the picture above that the blanket makes a sort of grid. The “smooth” squares in the blanket were knitted on the back side with the stitches P3, K1, P3 (purl 3, knit 1, purl 3). There are six of these squares in each row of the grid. I knitted my code on the back side so that the words would go from left to right. I coded letters into each square this way: P1, next two stitches are first digit of letter, K1, next two stitches are second digit of letter, P1.

I used two stitches for each digit of the letter, using a Base 5 code. I used P2 for 0 (since I was on the purl side); K2 for 1; yarn over, knit 2 together (ykt) for 2; ssk, yarn over (sky) for 3; and purl cable one stitch, holding to the back (cb) for 4. Here’s how the letters were made:

A: 01: p2 k2;
B: 02: p2 ykt;
C: 03: p2 sky;
D: 04: p2 cb;
E: 10: k2 p2;
F: 11: k2 k2;
G: 12: k2 ykt;
H: 13: k2 sky;
I: 14: k2 cb;
J: 20: ykt p2;
K: 21: ykt k2;
L: 22: ykt ykt;
M: 23: ykt sky;
N: 24: ykt cb;
O: 30: sky p2;
P: 31: sky k2;
Q: 32: sky ykt;
R: 33: sky sky;
S: 34: sky cb;
T: 40: cb p2;
U: 41: cb k2;
V: 42 – cb ykt;
W: 43: ykt cb;
X: 44: cb cb;
Y: 100: k2 p2 p2; (I knitted this as k2p1 (k1) p3, leaving the garter stitch in the middle.)
Z: 101: k2 p2 k2.

Here’s what I planned to have the blanket say (I added Alyssa’s name at the end when it was clear what that would be. Fortunately, I was knitting from bottom to top.):

Alyssa Karise,
Grace and Peace.
Grace and peace to you from God our Father and the Lord Jesus Christ.
Grace and Peace.

When I had the blanket all finished, ends sewn in, and I laid it out to take pictures — I discovered I’d left out a word! Urgh! But it’s still a Blessing Blanket. And I still thought about and prayed for Alyssa as I knitted. And it’s still warm and soft. I’m not going to say what word I left out, because I want to see if the baby’s parents can “read” it well enough to figure out! (I’m bad!) Astute readers of this blog who possess really really good eyesight might be able to tell as well.

To see how the coding actually looks, I took pictures of the top three rows. Here is AL – KA – GR:

Since the stitches are done on the purl side, k2 gives you straight bumps. So A = p2 k2 gives you a smooth panel, then bumps. L = ykt ykt gives you a hole from the yarnover, then two stitches together, in both sides. On the second row, K = ykt k2 combines both of those. Then we have A, which looks just like the first A. The third row has the same combination reversed in G = k2 ykt. Then R = sky sky. With sky, the stitches are knitted together before the yarn over, so the hole is on the right of the combined stitches.

The next section shows YS – RI – AC, and a fourth row, ND:

Y = k2 p2 p2, so I started on that first stitch I usually leave a purl stitch. So it looks the same as A, only shifted over one stitch to the left. S = sky cb shows us our final “digit”. The cable in back comes out as one stitch going over another with no hole. The second row is easier to see. R = sky sky, so you can see both sides have the hole on the right. Then I = k2 cb, and you can more easily see the cabled stitch crossing over. On the third row, we have A = p2 k2 and C = p2 sky. The fourth row, the end of the word AND, gives you a nice look at the cables again, with N = ykt cb and D = p2 cb.

I’ll give you the end of the top three rows, but I’ll leave it to the reader to work out that at least I didn’t make a mistake on the top of the blanket:

Making this was so much fun! In fact, I’ve been dragging my feet about sending it on. But tonight I noticed that the yarn label happens to have a pattern for a one-skein scarf, and I happen to have one skein left. So perhaps making myself a scarf out of this wonderful 85% cotton 15% angora yarn (Serenade) will remind me to send thoughts and prayers and blessings to my sweet little niece, Alyssa Karise.

And, meanwhile, my brother announced that his wife is expecting a baby. His baby needs a prime factorization blanket! I am swatching to figure out how best to accomplish this, and will definitely be letting my readers know!

My posts on Mathematical Knitting and related topics are now gathered at Sonderknitting.

More Mathematical Knitting

Monday, September 3rd, 2012

I’m a math nut. I’ve always said that my prime factorization sweater proves it.

I finished knitting the sweater in 2005. It shows the color-coded prime factorization of all the whole numbers from 2 to 100. I’ve shown it to lots of people since then, with mixed amounts of appreciation. In 2009, I finally posted a blog explanation of it and how it works.

Last April, I wore it to the US Science and Engineering Festival. I showed it to Ivars Peterson, manning the Mathematical Association of America booth. He tweeted one tweet with a link to my blog post, and the next day I got 28,000 hits on my website.

And the post got so much attention, this month it’s appearing in Hacker News! In print! I’m happy that people are finding out about it. It’s just goes to show that Math is Beautiful.

Now, there’s no way I’m ever going to make a replica of the original sweater. It took way too long. But since then, I’ve designed a t-shirt for sale to all on Cafepress. I’ve knitted a scarf that uses color-coded stripes to represent the prime factorization of numbers up to 50. And I’ve begun work on a cuff-to-cuff cardigan that also uses color-coded stripes, similar to the scarf. I hope it will go up to 100.

But for now I’m taking a break from knitting the prime factorization cardigan, because my little sister is having a baby!

I wanted to knit something special for the little one, but not so blatantly mathematical. I decided to use a mathematical code to knit a blessing into the blanket.

Here’s how it works. I’m using the same pattern I used to knit my son a cotton blanket 18 years ago. It’s a simple knit-purl pattern. I didn’t want lace, since I wanted it to function as a warm blanket. I gave it to him whenever he ate and managed to get him very attached to it!

I want to knit a code into the blanket. The layout is a basic grid. It mimics a plaid, but with knits and purls. I decided to focus on the stockinette sections that show up on one side. These sections are seven stitches across, with the stitch in the middle purled on every other row. There are six sections across in the grid and a total of 20 sections vertically down the blanket.

The baby is a girl, and her middle name will probably be Karise, coming from the Greek word for grace. I decided to use the Christian blessing that shows up many times in the New Testament: “Grace and peace to you from God our Father and the Lord Jesus Christ.” After all, what more could you want for a baby than grace and peace?

That’s 14 words, so I decided to put one word on each row of the grid, with the words “Grace and Peace” before and after, using all 20 rows. Each word is six letters or less, so I can use the six stockinette sections to highlight the letters.

Now, how to do the letters? Simple! Years ago, I did a library program where I showed the kids that they could use the ideas from the sweater to make codes using colors or shapes for letters. You start with a simple 1 to 26 code for the letters A to Z. Then I will convert the numbers to base 5 and I only need 5 different coded digits.

Here’s how the letters will be represented:

A – 01 B – 02 C – 03 D – 04 E – 10
F – 11 G – 12 H – 13 I – 14 J – 20
K – 21 L – 22 M – 23 N – 24 O – 30
P – 31 Q – 32 R – 33 S – 34 T – 40
U – 41 V – 42 W – 43 X – 44 Y – 100
Z – 101

Then I assign certain stitches to represent each digit. Since knitting is done from right to left, I’m going to work the stitches on the purl side, so when I look at them, they will read left to right.

Here’s the code I’m using, with two stitches for each digit.

0 = purl 2 (p2)
1 = knit 2 (k2)
2 = yarn over, knit 2 together (ykt)
3 = ssk, yarn over (sky)
4 = cable one purl stitch in back (cb)

Since the purl sections I’m using have 3 purl stitches, one knit stitch and then 3 purl stitches, I’m putting in the code this way: one purl stitch, then the first digit of the coded letter,
then one knit stitch, then the second digit of the coded letter, then one purl stitch.
I’m doing this on the middle row of the section of the grid.

I am working the code from the bottom of the blanket, so I had to list all the words in backwards order.

Here’s how it’s working out!

This picture shows the bottom three rows of the large grid. So I encoded the words “Grace and Peace.” Here’s the detail:

Looking at the first two sections of each word, on the top row, we have G = 12 = k2, ykt; R = 33 = sky, sky.
Second row has a blank section to center “AND,” then A = 01 = p2, k2.
Third row has P = 31 = sky, k2; E = 10 = k2, p2.

Here’s the middle section:

For the middle, on the top row, we have A = 01 = p2, k2; C = 03 = p2, sky.
Second row has N = 24 = ykt, cb; D = 04 = p2, cb
Third row has A = 01 = p2, k2; C = 03 = p2, sky

And finally, the last two sections in the row:

This just has the end of each word. On the first and third row, that’s E = 10 = k2, p2. We’ve got “blank” sections in the other slots.

Oh, and I should mention that on, I purchased some fabulously soft yarn on sale. It’s Artful Yarns Serenade, and it’s 70% pima cotton, and 30% angora. There’s one strand of pink, one of purple, and one of brown, which I thought more interesting than straight pink. It’s ending up so beautiful and wonderful to touch. I always say that knitting with soft yarn is like therapy. And this time, I get to knit in a mathematical blessing.

My posts on Mathematical Knitting and related topics are now gathered at Sonderknitting.

My Prime Factorization Scarf

Tuesday, August 21st, 2012

I finished it! Last week, I finished sewing the ends in on my new Prime Factorization Scarf.

The scarf is similar to my Prime Factorization Sweater, using a new color for each prime factor. For the scarf, though, instead of making a grid of squares representing each number, I used two-row stripes for each factor. I separated each number with two rows of black, which represented the number 1 (since 1 times anything doesn’t change the value.)

I like the way the scarf gives the flow of the numbers. You can look closely at the blue color for 2 and watch it repeat. Then notice how the pink color for 3 repeats a little more slowly. And 5 a little more slowly than that. The scarf goes all the way up to 50.

Here are some sections up close. First, this picture shows 1 through 21:

2 is blue.
3 is pink.
4 = 2 x 2, so it’s two stripes of blue.
5 is yellow.
6 = 2 x 3, so it’s a stripe of blue and a stripe of pink.
7 is purple.
8 = 2 x 2 x 2, so it’s three stripes of blue.
9 = 3 x 3, so it’s two stripes of pink.
10 = 2 x 5, so it’s a stripe of blue and a stripe of yellow.
11 gets a new color, green.
12 = 2 x 2 x 3, so it’s two stripes of blue and a stripe of pink.
And so on….

Here is a picture showing 17 (light pink) through 35:

And finally, 33 to 50:

My earlier posts explained why I chose the pattern I did. I wanted the scarf to be reversible, but it’s not quite as easy to read as plain garter stitch stripes.

What’s next? A cuff-to-cuff cardigan! Only, I want to go higher than 50, so I decided to combine factors in one stripe — unless you have perfect powers of a number. Here’s a preview. I’m working on 33 now. (You can see that since 32 = 2^5, it’s 5 rows of blue.) It’s going to be flamboyantly bright, but I plan to wear my primes with pride!

My posts on Mathematical Knitting and related topics are now gathered at Sonderknitting.

Prime Progress

Friday, May 18th, 2012

Woo-hoo! After getting my prototype Prime Factorization t-shirt from my new Cafepress Shop, I tweaked the colors to make the chart brighter. I also made shirts on different colored backgrounds. As luck would have it, the new shade for 2 almost perfectly matches the “Caribbean Blue” background. My new revised shirt came this week, and I love it!

For those just coming in on this, the chart is 10 rows of 10, beginning at the bottom left. (Because I can’t bring myself to have higher numbers down lower on the shirt.) Each prime number gets its own color, and the prime factors of each number are displayed by color. Unlike the sweater, the numbers are listed on the shirt.

Like the sweater, I couldn’t resist putting rows of 8 on the back. And of course, I had to list those numbers in their Octal representation. But since that adds to the cost, I’m also offering t-shirts that have only the chart on the front.

Now, as long as I was so happily wearing my prime factorization t-shirt, I had to spend some time making progress on my prime factorization scarf. The biggest problem with the scarf is that I need to carry around lots of skeins of yarn. Fortunately, I ordered a Prime Factorization Tote Bag from my Cafepress Shop! (The pictured one was ordered before I brightened up the colors.)

I am super happy about how the prime factorization scarf is turning out. The original sweater is kind of pointless if you don’t know what it represents, but the scarf is aesthetically pleasing totally aside from the mathematics.

Here is my progress earlier this week, up to 24. (Today I finished 30, and, honestly, it’s hard to stop, because it’s so much fun to see how the next number will turn out!)

This one starts at the bottom. Though with a scarf, you can hold it any direction you like.

Once again, the background color, black, represents 1. It’s used between the other numbers.

The first stripe of blue is our first prime, 2.

Then we have pink for 3.

4 = 2 x 2. It’s not quite as easy to tell on the scarf, but the next blue stripe is twice as wide as the original.

5 gets a new color, yellow.

6 = 2 x 3, so a stripe with blue, then pink.

7 gets purple.

8 = 2 x 2 x 2, so that stripe of blue is three times as wide as the original.

And so it goes. I love the way the colors flow. You can quickly see that blue is showing up every second stripe, and that every second blue stripe is fatter. You can see the pinks showing up every third stripe and the yellows every fifth. As I said, I think it makes a lovely art object totally apart from the math behind it. And the math makes it completely cool.

Also, with a scarf, you don’t have to decide your colors ahead of time. I am using a certain progression. I’m afraid going to 100 is going to be ridiculously long, but I may do it anyway. After all, I’m doing it more for the math than anything else. But when I’m done, I’m planning to make a cuff-to-cuff cardigan using the same design, and that one cannot go so high.

I’ll continue to show my progress. Such fun!

My posts on Mathematical Knitting and related topics are now gathered at Sonderknitting.

My Prime Factorization T-Shirt Shop Is Ready!

Wednesday, May 9th, 2012

My Prime Factorization T-shirt Shop is ready!

Now, the motivation was that when the math community found out about my Prime Factorization Sweater, many commenters said I should make a T-shirt. I “happen” to have several of the charts already created in Word, because I’ve written a children’s book about using these ideas to learn about other mathematical bases and make cyphers and patterns using the mathematical principles. So I used two of those charts to make a shirt. But I did want to see if the colors came out distinct enough before I offered it for sale.

Monday night, the shirt I ordered arrived, so I wore it to work yesterday:

And here I am among the Math books:

On the back, as with the sweater, I’ve got rows of 8, so you can see that the patterns change.

Now, there were two things I wasn’t quite happy about with the shirt.

First, one thing I was happy about was that the colors came out exactly as they looked when I printed out the charts. However, that was also the first thing I was not happy about. The blue shade for 2, on my computer screen, is nice and bright and easy to spot. On the print-out, and on the shirt, it looks much darker.

The second thing I was unhappy about was that the numbers were blurry. This was because I hadn’t been able to save my Word table as a jpeg file. My son came up with the solution of taking a screenshot and merging the two pictures into a jpeg. It was good enough, but I really noticed the little imperfections.

Then, at work, wearing the shirt, I had a brainstorm. Surely in publisher, you can turn files into jpeg files? Sure enough! So yesterday evening I went home, opened my book manuscript, and pasted the prime factorization table into publisher. It worked! My test shirt hasn’t arrived yet, but I’m confident the numbers will be more clear.

While I was at it, I changed the colors, and lightened up some factors that are used several times in the chart, particularly the blue for 2. Since my graphic looks different when it’s printed, I’ll post a picture of how the print-out looks, because that’s how it will look on the shirt:

I also added various colors, by popular demand. I now have a Caribbean Blue shirt on order with the new charts.

One other thing I should mention. For “Super Geeks” (like me), I did put rows of 8 on the back. All the charts have the numerical values under the color code, but on the back, I gave those numbers their Octal representation. So after 7 comes 10, after 10 comes 11, after 17 comes 20, after 77 comes 100, and so on. A couple times, when I was looking at the back, I forgot I was looking at the back and thought I had factored incorrectly! With the colors, you could use this as a handy-dandy way to convert from decimal to octal! (Just what everyone needs, right? But if you’re ever on an alien planet….)

I do like the way the two charts with the same colors show how the patterns change. Particularly look at yellow (5). In the decimal chart, because it’s a factor of 10, it lines up. In the octal chart, because it’s relatively prime with 8, it does not line up.

So, I’m looking forward to my new shirt coming in! And I do feel ready to offer my shirts for sale!

The URL is

Prime Factorization Swatches

Saturday, May 5th, 2012

I finished three swatches and decided on how I’m going to approach my new Prime Factorization Scarf.

First, I tried garter stitch. It’s a reversible stitch, and I thought it would work for the scarf. No pun intended, I thought I’d begin with the primary colors, since they are clearly “red,” “blue,” and “yellow.” Here’s how that swatch turned out:

The colors do stand out in this version. Black is 1, the background color. The pattern starts on the left. 2 is red. One ridge clearly stands out for the factor. When you get to 1 again, you stop multiplying and start a new number. Primes will always be one ridge. Next is 3, which is blue. Then comes 4, clearly showing as two ridges of red, 2 x 2. Then black, so you start a new number. Then comes 5, a new color, yellow. Then black. Then we have a ridge of red with a ridge of blue, 2 x 3 = 6. A ridge of black. Then 7, a new color. Black. Three ridges of red, 2 x 2 x 2 = 8. Black. Two ridges of blue, 3 x 3 = 9. Black. A ridge of red and a ridge of yellow, 2 x 5 = 10.

What I like about this swatch? The colors pop out and clearly show how many of each factor you want.

Problems with this swatch? Well, I completely forgot that garter stitch with colors is not reversible. Here’s the other side:

The garter stitch pattern would work great in a sweater, where you only see one side. But a scarf is better when it’s reversible, since it’s not easy to keep only one side of a scarf showing.

One other problem was that I didn’t like the colors. In the picture on the web, the red looked like a pretty cherry red. In real life, it was so bright, it almost glowed in the dark. Next to black, it feels glaring.

So I decided to experiment with the colors I think are the prettiest of all the ones in the box. After all, the color for 2 is going to get used in every other stripe. Might as well use a color I like to look at, right?

I needed to pick a stitch that would be reversible in color. I chose the Double Seed Stitch, which gives a nice textured look. You alternate two knit stitches with two purl stitches, and you do two rows that line up with each other. Then you do two rows with the stitches staggered from the first two — The knit stitches in the two top rows are lined up with the purl stitches in the bottom two rows, and the purl stitches in the two top rows are lined up with the knit stitches in the bottom two rows.

You can’t really tell the colors I used in the next swatch, but it’s a turquoise for 2 and pink for 3, yellow for 5, and purple for 7. I got happier and happier as I knitted. I think this is beautiful, and it will be the pattern I use for the scarf. Here’s that swatch:

Now, I acknowlege that it’s not nearly as easy to tell exactly where the numbers separate or exactly which factors are in the number. But it’s pretty. And I know which factors are where. And it’s completely reversible. The back looks exactly the same as the front.

I did one more swatch, to be absolutely sure I wanted to use a black background. I also wanted to see if using larger needles would make the fabric more drapey. The yarn band suggests size 8 needles, and that’s what I’d been using, and I think it would be nice for a sweater. But for a scarf, I’d like a little less firmness. So I made the next swatch with a cream-colored background and size 10 needles, but the same stitch and the same colors for the numbers. Here’s that swatch:

Yes, this combination is pretty. But I think it reminds me too much of my original prime factorization sweater, and I’m ready for something different. So I’m going to go with the black background.

So I’ve begun! I’m using Size 10 needles, a black background, double seed stitch, and 26 stitches across. (The swatches used 20 stitches.)

Oh, one more thing: I hereby resolve that I will, I WILL, sew the ends in as I go, so that I don’t have to do them all at the end, like I did with the sweater. (Sigh. The worst thing about this whole project!)

I also plan to make a black edging along the sides, to hide the carried-along yarn. I can practice on the swatches.

And while I’m knitting, my mind will be spinning with ideas for a cardigan.

Stay tuned and watch my progress! One of the fun things about it is that I can wait to choose colors as I go. I don’t even have to stop at 100….

My posts on Mathematical Knitting and related topics are now gathered at Sonderknitting.

Ready to Start My Prime Factorization Scarf!

Wednesday, May 2nd, 2012

My yarn arrived tonight! 26 shades of Plymouth Encore yarn (on sale at, so I can make a Prime Factorization Scarf that goes all the way up to 100!

Now, a lot of the shades ended up looking more alike than I hoped they would. But I can always hold those toward the end where they only turn up once. I also didn’t realize what large skeins I was getting — I will need to make a sweater after this, because I’m going to have all kinds of leftover yarn. But I can change the color scheme to keep it interesting.

My mission first: Decide which colors will be most dominant. I’m planning on black for 1 this time, but I’m going to swatch out some different combinations for 2, 3, 5, and 7, to decide how I like it. I was planning on red for 2, but it’s so bright — I might not want that much red in the scarf. And I really like the turquoise blue that came. So we shall see… I’ll make some small swatches before I try the actual scarf.

If anyone wants to play along and make a scarf with me, let me know! It might be a lot smarter to make this as a leftover-yarn project and use up old yarn, instead of buying all the same yarn. I wish I’d thought of that! Anyway, I will think in terms of using the yarn for a cardigan later. For now, I’m looking forward to playing with some swatches!

My posts on Mathematical Knitting and related topics are now gathered at Sonderknitting.

Prime Factorization Knitting Revisited

Sunday, April 29th, 2012

Yesterday I went to the US Science and Engineering Festival in DC, and made sure to stop at the Mathematical Association of America booth. I knew they’d be there because every day I make sure to do MAA Minute Math.

I was hoping it would be cool enough (weatherwise) to wear my prime factorization sweater (For the explanation, follow the link!), and to my joy it was. I was happy to get a picture taken at the MAA booth.

Well, that got the attention of many more math people, and today I found four new comments on my blog post about the sweater and a page about me on Hacker News!

Now, the good people at Hacker News did misread my age, so I will post something I just realized that will be true this year after my younger son and I have our birthdays. (I was so delighted when I realized it, I ran to tell my son, not realizing he’d just gone to bed.)

My age will have five prime factors.
My oldest son’s age will have four prime factors.
My youngest son’s age will have three prime factors.

A picture of the three of us should enable you to narrow it down. (I am not 72, and my youngest son is not 8.)

I’ll add one more cool set of facts to definitely set our ages:

In the year my oldest son was born, my age had four prime factors (as his does now).
In the year my youngest son was born, my age had three prime factors (as his will this year).

Let’s see. My youngest son’s age is still ambiguous. So I’ll add the clue that there are only three distinct prime factors in all the expressions above. That should do it.

So, all this establishes that I was thinking about prime numbers yesterday. And, yes, I think it’s time to make a prime factorization cardigan, which I can wear in warmer weather.

Some have said I should sell these. But let’s be honest. Having to buy all those shades of yarn costs around $100. Then it was definitely not my only knitting project, but it took me more than a year to knit. (Fun time, but not worth spending if it were for monetary gain and not for the fun of it.) Then it took me more than a month just to sew in all the yarn ends. Granted, if I made more with the same color scheme, that would spread out the cost. But by the time I finished, I’d had quite enough of the project. It has taken ten years for me to be at all interested in doing anything similar, and I’m NOT going to use the same yarn and color scheme as before; you can be sure of that.

With a cardigan, you wouldn’t have room for a chart on both sides. So I was thinking about how else to express it. Last night, I ordered some Plymouth Encore yarn from to make a scarf.

Why Plymouth Encore? Well, first, it’s on sale right now. Needing 26 different colors to go up to 100, any savings per ball helps. I also decided that my cotton sweater (the original was made in Cotton Classic), while soft and comfortable, is a little bit droopy, and wasn’t the greatest choice for the intarsia work. Wool by itself risks being too scratchy. Most of all, this had enough colors, which I hope will be distinct.

This is my plan this time:
I think I’ll use a black background this time. I don’t look good in black is the one reason I didn’t use that on my sweater. (The original partial picture of a blanket that gave me the idea used a black background.) But in a scarf, the background won’t be as prominent.

I’m thinking I’ll use garter stitch, with two rows and one ridge for each factor. I will probably put two stitches of black (one) along the sides, in order to (I hope) hide the two and three factor colors being carried along the edge of the sweater. (I absolutely WILL sew in ends as I go this time. I will. I WILL!)

So here’s how it will work. I’ll start with however many rows of black looks good at the beginning. This is 1. Then I’ll choose a color for 2 and knit two rows (one ridge) in that color. Then I’ll do two rows of black. That represents a factor of 1, and also tells you that we’re starting on a new number. 3 will get two rows of a new color. Then two rows of 1. 4 is 2 x 2. So 4 will be expressed with four rows (two ridges) of the 2 color. Then two rows of 1. Then a new color for 5. Then two rows of 1. Then 6 = 2 x 3, so two rows of 2 directly followed by two rows of 3. Then two rows of 1.

Get the idea? Numbers with lots of prime factors will take up more space than prime numbers.

Mind you, I’ll swatch it out, with some different color choices, and see what looks best. (You definitely want your favorite colors as 2 and 3.) I will post pictures when I get there.

Once I have a scarf done? Well, what I might try with a cardigan is a chart like the old sweater on the back (in new colors and yarn) and maybe stripes as in the scarf on the front sides. Or maybe I’ll be sick of it and give it a rest for awhile.

Based on the new comments, it’s time for me to design a t-shirt! Stay tuned. I have written a children’s book which I called Colors and Codes that talks about using these ideas to make cyphers and patterns using colors or shapes combined with math. As part of the book, I made several charts on my computer. I will see how hard it is to transfer these charts to a t-shirt in Cafe Press.

By the way, I haven’t tried to sell this book yet. I had been working on selling a middle grade novel, and lately I’ve been letting both efforts rest while I dealt with some medical issues. But if anyone knows of an agent or a publisher who’d like to take on something a little unorthodox but extremely cool to math geeks, let me know!

It’s been about ten years since I designed and knitted the sweater. (So I was WAY young then!) Let me stress that the idea of visualizing the prime numbers through colors in knitting was not my own. By all means, spread the word! The article I read (and I should definitely track it down. It was in Interweave Knits in the late 90’s or 2000 or so.) talked about how the blanket that had been made inspired kids who didn’t think they were good in math. As I say in my book, you can attach the numbers to the letters of the alphabet and use these ideas to knit or color messages into things. The sky’s the limit, and it’s lots of fun.

Once I have some swatches, I’ll take some pictures and post the results!

Edited to add: I found the inspiration! It was an article in the Fall 2003 issue of Interweave Knits, called “geekchic” by Brenda Dayne, regarding the work of Pat Ashcroft and Steve Plummer. They have a fabulously cool website at Here’s what the article said about an afghan they created:

“Across the Atlantic Ocean and far from the research laboratories and hallowed halls of Academia, a young girl, age thirteen, stands mesmerized in front of a knitted afghan displayed at the annual North-East Math Fair in Lancashire, England. Constructed of one hundred brightly colored squares, the intricately striped fabric is the creation of Pat Ashforth and Steve Plummer ( Knitters, teachers, mathematicians, and partners, Pat and Steve have found that basic mathematical principles make for beautiful knitwear designs, and that knitting is an excellent way of explaining complex theorems to their students.

“Vibrating with color, and reminiscent of African Kente cloth, the Counting Panes afghan is so beautiful it’s hard to accept that it was created as a teaching tool. Within its one hundred brightly colored squares, in ten columns and ten rows, however, lie lessons in multiplication, division, pattern, and numerical relationships… If a square contains yellow, it contains a number divisible by two, if it contains red, then the number divides by three. The more colors in a square, the more numbers it divides by.”

Now, they only had a photograph of a very small part of the afghan, so I couldn’t see how it worked. That part would not work on my sweater at all — there are several squares that appear to just be dark blue, and it’s stated elsewhere that green always appears with baby blue. So maybe that quilt is just showing factors of numbers, and not the prime factorization? Maybe beyond a certain point primes don’t get new colors?

But anyway, having the fondness for math that I do, that much information made me realize that I could knit a prime factorization chart. But I wanted to wear it, not just look at it! I still can’t make sense of what, exactly, their afghan was doing, but they are the ones who gave me the idea behind my design. I graphed it out, figured out how many stitches across I needed, and then found a basic sweater pattern from the book Picture Knitting to use as my canvas. Thank you so much for the germ of the idea!

My posts on Mathematical Knitting and related topics are now gathered at Sonderknitting.

Review of You Can Count on Monsters, by Richard Evan Schwartz

Monday, September 12th, 2011

You Can Count on Monsters

The First 100 Numbers and Their Characters

by Richard Evan Schwartz

A. K. Peters, Ltd., Natick, Massachusetts, 2011.
Starred Review

When I first heard of this book, I was delighted, and rushed to order my own copy. I was even more delighted when I read the book. I requested that the library system order it as well. This book would have been absolutely perfect when my sons were young and exploring numbers. I hope I get a chance to share it with a child.

I love it so much because of my experience making my prime factorization sweater. I chose a color for each prime number, then made a chart of all the natural numbers up to 100, showing their prime factorization with colors. I loved all the patterns that resulted.

Richard Evan Schwartz uses a similar idea, but adds a lot of creativity: For each prime number, he creates a monster! Then composite numbers are shown with the monsters from their prime factorization interacting together. It’s a lot of fun to look through the pictures and see the way he’s worked in the monsters. He’s also got an arrangement of dots on each page that demonstrates more about the number and the way it’s composed.

He says he created the monsters to explain prime numbers and factoring to his daughter, and I would love to share this book with a child. You can look at it again and again.

There’s a lovely simple explanation of multiplication and factoring at the front of the book. Then he explains the method behind the monsters:

“Each monster has something about it that relates to its number, but sometimes you have to look hard (and count) to find it.”

“For the composite numbers, we factor the number into primes and then draw a scene that involves the monsters that match those primes.

“It isn’t always easy to recognize the monsters in a scene. For instance, here is the scene for the number 56. You should see three 2-monsters buzzing around one 7-monster. Recognizing the monsters in the different scenes is part of the fun of the book!”

This book would also be great support for a child learning the multiplication tables. If you visualize monsters, they’ll be much easier to remember!

Most of all, I love the way this book showcases the playful, creative, and beautiful side of mathematics. You can count on Monsters to show you just how much fun math can be!

Buy from

Find this review on Sonderbooks at:

Disclosure: I am an Amazon Affiliate, and will earn a small percentage if you order a book on Amazon after clicking through from my site.

Source: This review is based on my own copy of the book.