Last Sunday my husband and sat in front of my old laptop (our only computer) and started a new cross-stitch pattern.
It's based on the Sieve of Eratosthenes which is a visual/tabular way to identify prime numbers. It's been modified a little bit. Instead of just identifying primes, it will also represent the factors of composite numbers by different colors.
The pattern looks quite complicated, but it doesn't have to be. We've made it in such a way that you can make it super-complicated, will of the factors for numbers up to 120 identified with different color. Or you can make it much more simple by deciding to just mark primes (the factors) up to a certain number.
I've started to make one for our baby's room. She was due last Sunday and still isn't here. It's in the colors of the nursery (lilac, sage, and tan). We have used 6 colors (aside from black and white, which will eventually show up).
2 = Darker purple
3 = Light green
5 = Darker green
7 = Light purple
11 = Darker tan
all other primes = Tan