[dskloet]

I solved it in less than 15 minutes while walking my dog, no pen or paper. But I wouldn't claim to be a random person without math skills. And my very first guess was correct.

It was a fun puzzle though and I'm surprised I didn't know it already. Thanks for sharing.

[wrasee]

My dog solved it in less than 14 minutes, no pen or paper, and no fingers.

Seriously though, nice work.