This comment does a great job of clarifying the picture: https://news.ycombinator.com/item?id=17106193 https://news.ycombinator.com/item?id=17106193. It's effe

This comment does a great job of clarifying the picture: https://news.ycombinator.com/item?id=17106193 https://news.ycombinator.com/item?id=17106193. It's effectively a visualization of gcd(x,y), and has almost nothing to do with primes. Once you realize that, it's a lot easier to reason about a lot of the patterns, although it is still a pretty interesting visualization.