A Better Proof

One of any three consecutive numbers must be divisible by 3.

2^n-1, 2^n, 2^n+1 are three consecutive numbers.

2^n-1 is not divisible by 3 because it it prime.

2^n is not divisible by 3 because it is divisible by 2 and its powers.

Then 2^n+1 must be divisible by 3.

Therefore, 2^n+1 is composite.

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• 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