Sorry, there was a little error. At first there was a proof

for such fact that p is composite; then I obtained yet

stronger result (namely 3|p), but I didn't update the

proof... :-)

***>Proof:

***

>

>Let p=(2^n+1)/n is prime greater than 3. n must be odd, so

>2^n+1 is divisible by 3; p is prime, hence, n is divisible

>by 3.

You should read:

***

Proof:

Let p=(2^n+1)/n isn't divisible by 3. n must be odd, so

2^n+1 is divisible by 3; hence, n is divisible by 3.

***

Best wishes,

Andrey

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