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%I #23 Sep 08 2022 08:45:33
%S 7,31,8191,2305843009213693951
%N Primes of the form 2^(2p - 1) - 1, where p is prime.
%C Primes in A139287.
%C This sequence is a subsequence of A000668. From A000043, a(5) = 2^3217 - 1.
%C The next term a(6) is an unknown Mersenne prime. [_Washington Bomfim_, Nov 18 2009]
%C a(5) has 969 digits. - _Vincenzo Librandi_, Dec 14 2010
%C The first three terms can be written as (n^3 - 1)/(n - 1) for some n. [_Arkadiusz Wesolowski_, May 09 2012]
%H Michel Marcus, <a href="/A139314/b139314.txt">Table of n, a(n) for n = 1..5</a>
%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Mersenne_prime">Mersenne prime</a>
%o (Magma) [a: p in PrimesUpTo(4200) | IsPrime(a) where a is 2^(2*p-1)-1]; // _Vincenzo Librandi_, Dec 14 2010
%Y Cf. A139286, A139287.
%Y Cf. A000668, A000043. [_Washington Bomfim_, Nov 18 2009]
%K nonn
%O 1,1
%A _Omar E. Pol_, Apr 13 2008
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