Certified math nut Sondra Eklund has made an awesome sweater. Before you read her explanation, take a look at it and see if you can figure out how it works.
Of course, the synesthete in me says her color choices are all wrong. But she’s coloring a different animal here (primes, not numerals) so there’s no real way to be “right”. Regardless, I want this as a T-shirt!