mod 8?

Hardly the 'mystery of number theory' the poster was talking about. There was no 'mod 8' syntax expressed in the example.

Yes, it is http://en.wikipedia.org/wiki/Modular_arithmetic

But you don't need to write "mod 8" in a congruence class

Oh, you want "the mystery of number theory" you can start with http://en.wikipedia.org/wiki/Fermat%27s_little_theorem

It was solved, and he (Fermat) was likely wrong, given the resulting proof.

(5 + 3) % 8 = 0 is not the same as 5 + 3 = 0

I'm not looking for mystery, I'm wondering why people think it exists, and are faking its existence by being imprecise.