Let p,q positive prime numbers, q>5. Prove that if
q∣(2p+3p) then q>p.
First, it's clear that p≠q because, using Fermat's little theorem, 2p=2modp and 3p=3modp, therefore 5=0modp false because q>5.
Now suppose q<p. I tried to analyse 2p+3pmodq but I didn't get a contradiction.
Answer
HINT:
For p>2
(−32)p≡1(modq)
⟹ordq(−3/2)|(p,q−1)
But As p is prime, ordq(−3/2)=1 or p
ordq(−3/2)=1⟹−3≡2(modq)⟺5≡0⟺q|5⟹q=5
Else p|(q−1)
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