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 A139297 #10 Jul 10 2025 16:02:20 %S A139297 15,4095,1152921504606846975, %T A139297 7237005577332262213973186563042994240829374041602535252466099000494570602495 %N A139297 a(n) = 2^(2p - 1)/2-1, where p is the n-th Mersenne prime A000668(n). %F A139297 a(n) = 2^(2*A000668(n)-1)/2-1 = A139296(n)-1. %t A139297 a[n_] := 2^(2^(MersennePrimeExponent[n] + 1) - 4) - 1; Array[a, 4] (* _Amiram Eldar_, Jul 10 2025 *) %Y A139297 Cf. A000668, A139294, A139295, A139296, A139298, A139299, A139300, A139301, A139302, A139303, A139304, A139305, A139306. %K A139297 nonn %O A139297 1,1 %A A139297 _Omar E. Pol_, Apr 13 2008 %E A139297 a(4) from _Amiram Eldar_, Jul 10 2025