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 A013208 #9 Oct 22 2023 11:38:11
%S A013208 0,1,-2,3,-8,45,-272,1743,-13568,125625,-1290752,14554683,-181296128,
%T A013208 2473184805,-36501112832,579439207623,-9859508338688,179018972217585,
%U A013208 -3453141256896512,70518070842040563
%N A013208 Expansion of e.g.f. log(sech(x) + tanh(x)).
%e A013208 x - 2/2!*x^2 + 3/3!*x^3 - 8/4!*x^4 + 45/5!*x^5 ...
%t A013208 With[{nn=20},CoefficientList[Series[Log[Sech[x]+Tanh[x]],{x,0,nn}],x] Range[0,nn]!] (* _Harvey P. Dale_, Oct 22 2023 *)
%K A013208 sign
%O A013208 0,3
%A A013208 Patrick Demichel (patrick.demichel(AT)hp.com)
%E A013208 a(0)=0 inserted and title improved by _Sean A. Irvine_, Aug 01 2018