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 A304980 #13 Jun 25 2018 03:52:06 %S A304980 -2,7,-77,1657,-58457,3056557,-221729237,21295269457,-2614745018417, %T A304980 399460073350357,-74300372446261997,16529958050063939257, %U A304980 -4333993989483331875977,1322511243007573825356157,-464663077436832702395156357,186233354336664458732835601057 %N A304980 a(n) = 4^n * (1 - 4^n) * Bernoulli(2*n) / (2*n) + EulerE(2*n). %F A304980 a(n) = (-1)^n * (A000182(n) + A000364(n)). %t A304980 Array[4^#*(1 - 4^#) BernoulliB[2 #]/(2 #) + EulerE[2 #] &, 16] (* _Michael De Vlieger_, May 24 2018 *) %o A304980 (PARI) a(n) = 4^n * (1 - 4^n) * bernfrac(2*n) / (2*n) + 2*imag(polylog(-2*n, I)); \\ _Michel Marcus_, May 30 2018 %Y A304980 Cf. A000367 (Bernoulli numerators), A002445 (Bernoulli denominators), A028296 (EulerE(2*n)), A241242. %Y A304980 Cf. A000182 (tangent numbers), A000364 (secant numbers). %K A304980 sign %O A304980 1,1 %A A304980 _Daniel Suteu_, May 22 2018