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Old 2008-05-30, 00:30   #9
ATH
Einyen
 
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Dec 2003
Denmark

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Question solved.

I found a factor of 2p-1*(2p-1) + 1 for p=132049 with gmp-ecm:
194528547122653

So of the 44 known perfect numbers P=2p-1*(2p-1), P+1 is only prime for p=2,3,13 and 19.

Last fiddled with by ATH on 2008-05-30 at 00:31
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