[userbinator]

I suspect it was partly inspired by https://en.wikipedia.org/wiki/Illegal_number#Illegal_primes

[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 :)