see here for two solutions.
Prove that for ANY integer n, has no prime divisors of the form 6m-1.
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Attempt:
Let p be a prime divisor of .
Then ≡ 0 (mod p)
=> ≡ 0 (mod p)
=> ≡ 1 (mod p)
Let = order of n mod p
=> |3
=> = 1 or 3
Now I'm stuck here. How to finish the proof from here?
Any help is greatly appreciated!
[also under discussion in math links forum]