[dmurray]

The first version of this I saw came from the webcomic in this reddit thread about a prime number that looks like a giraffe.

After one commenter showed off this technique, someone else found a minimal prime giraffe: 7.

[0] https://www.reddit.com/r/math/comments/7qpfls/does_there_exi...

[geonnave]

primg is, indeed, inspired by the prime giraffe :)