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 A139296 #12 Jul 10 2025 16:02:45 %S A139296 16,4096,1152921504606846976, %T A139296 7237005577332262213973186563042994240829374041602535252466099000494570602496 %N A139296 a(n) = 2^(2p - 1)/2, where p is the n-th Mersenne prime A000668(n). %C A139296 a(5) has 4931 digits and is too large to include. - _R. J. Mathar_, May 30 2008 %F A139296 a(n) = 2^(2*A000668(n)-1)/2. %t A139296 a[n_] := 2^(2^(MersennePrimeExponent[n] + 1) - 4); Array[a, 4] (* _Amiram Eldar_, Jul 10 2025 *) %Y A139296 Cf. A000668, A139286, A139294, A139295, A139297, A139298, A139299, A139300, A139301, A139302, A139303, A139304, A139305, A139306. %K A139296 nonn %O A139296 1,1 %A A139296 _Omar E. Pol_, Apr 13 2008 %E A139296 One more term from _R. J. Mathar_, May 30 2008