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If $p\equiv3\pmod{4}$ and $q=2p+1$ is a prime then $q|(2^p-1)$ if $2^p-1$ is composite.

Also, prove that there are infinitely many primes $p$ for which $2^p-1$ is composite.

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    please read in place of multiple, 2^p -1 is composite2011-09-17
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    Can you state your question in the form of a question?2011-09-18

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