Sunday 24 June 2018

Odd number $N$ which does not divide $2^k-1$


Prove that there does not exist a composite odd number $N > 1$ which does not divide $2^k-1$ for $k = 1,2,\ldots,N-2$.




I conjectured this result, but wasn't sure how to prove it. I tried it for many cases and it seems to be true.

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