Question

prove 7 divides 2n-1 = 3divides n

Answer 1

Prove tht \[\forall n \in \mathbb{N} , 7|(2^n-1) <=> 3|n\]

Answer 2

a hint is to look at the multiplication table (for \[\mathbb{Z}/7\mathbb{Z}\] and computer
powers of 2 mod 7, and to notice how they repeat