Mersenne primes

A Mersenne prime is a prime number of the form 2^n-1; for instance, 7 = 2^3-1.
Prove that if 2^n-1 is a prime then 2^n+1 is not a prime for n>2.
Is there a name for the primes of the form 2^n+1?

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• 回复：Mersenne primes -passenger101- ♂ (443 bytes) () 01/29/2008 postreply 09:07:51

• A Better Proof -群众丁- ♂ (342 bytes) () 01/29/2008 postreply 10:26:32

• 回复：A Better Proof -passenger101- ♂ (10 bytes) () 01/29/2008 postreply 10:34:51

• Great! -eom -yma16- ♂ (0 bytes) () 01/29/2008 postreply 11:19:01