[atsushin]

Hi! Just a question, since I've never been good with proofs. Why use the modulo operator in the while-loop? Couldn't we just test if i != j?

[tomjakubowski]

The modulo represents the cycle.

Maybe it would be helpful to rewrite the loop with a condition as you described, and %= i and j with n after incrementing (by 1 or by 2) both variables in the loop body.