Thanks to the Internet, I learned about an interesting thing that a man named Stanislaw Ulam came up with.

Basically, he took the number 17, and then wrote it in the center of what will become a grid. Then he wrote the next consecutive number, 18 to the right of 17 it. 19 above 18, etc:

21-20-19

22-17-18

23-24-25

This grid continued to spiral up until the number 272. What is interesting about this grid is that when Ulam figured out all of the prime numbers between 17 and 272, many of the primes formed diagonal lines. This included one giant diagonal that consists of every number from the bottom left to top right corners. [In my small example above, you can see this with 23, 17, and 19.]

Interesting!