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 A003702 M5110 #24 Oct 29 2023 01:42:32
%S A003702 1,-1,21,-141,10441,-183481,29429661,-987318021,276117553681,
%T A003702 -15085947275761,6514632269358501,-526614587249608701,
%U A003702 324871912636292700121,-36433570919762397948841,30417659816002454665514541
%N A003702 Expansion of tan(x)/cosh(x).
%D A003702 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A003702 Vaclav Kotesovec, <a href="/A003702/b003702.txt">Table of n, a(n) for n = 0..240</a> (first 50 terms from T. D. Noe)
%F A003702 a(n) ~ (2*exp(Pi/2) + (exp(Pi) - 1)*(-1)^n) * (2*n+1)! * 2^(2*n+3) / ((1+exp(Pi)) * Pi^(2*n+2)). - _Vaclav Kotesovec_, Feb 16 2015
%t A003702 Tan[ x ]/Cosh[ x ] (* Odd Part *)
%t A003702 nn = 20; Table[(CoefficientList[Series[Sech[x]*Tan[x], {x, 0, 2*nn+1}], x] * Range[0, 2*nn+1]!)[[n]], {n, 2, 2*nn, 2}] (* _Vaclav Kotesovec_, Feb 16 2015 *)
%K A003702 sign
%O A003702 0,3
%A A003702 _R. H. Hardin_, _Simon Plouffe_