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Old 2008-05-27, 14:36   #2
R.D. Silverman
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Nov 2003

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Originally Posted by Housemouse View Post
If P is an even perfect number greater than 6, P-1 is always composite divisible by nine. Is it known which perfect numbers are prime for P+1?
Clearly not. We don't even know whether the Mersenne primes are
infinite in number.
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