This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A277634 #11 Nov 12 2016 21:40:24 %S A277634 7,127,2147483647,170141183460469231731687303715884105727 %N A277634 a(n) = 2^A000668(n) - 1. %C A277634 The terms of this sequence are sometimes called "Double Mersenne numbers" (cf. A263686). %C A277634 Agrees with A077586 in the first four terms, but then the two sequences differ for the first time at n = 5, because prime(5) = 11 is not in A000043. %C A277634 a(5) is too large to include in data section (see A276641). %C A277634 a(n) = A263686(n) iff a(n) is prime, which is the case iff A000668(n) is in A103901. %C A277634 Agrees with A263686 at least in the first four terms. - _Omar E. Pol_, Oct 24 2016 %F A277634 a(n) = A000225(A000668(n)). %o A277634 (PARI) forprime(p=1, 11, if(ispseudoprime(2^p-1), print1(2^(2^p-1)-1, ", "))) %Y A277634 Cf. A000043, A000225, A000668, A077586, A103901, A263686, A276641. %K A277634 nonn,bref %O A277634 1,1 %A A277634 _Felix Fröhlich_, Oct 24 2016