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 A009254 #13 Mar 07 2018 19:19:21
%S A009254 1,1,1,0,-3,12,117,336,-903,-2096,111529,1043328,687093,-29488704,
%T A009254 320199453,8894706432,44530596081,-389860902656,254346923089,
%U A009254 170568226222080,2006766293627373,-6327905330549760,-141849542553657147
%N A009254 Expansion of exp(tan(x)/cosh(x)).
%t A009254 With[{nn=30},CoefficientList[Series[Exp[Tan[x]/Cosh[x]],{x,0,nn}],x] Range[0,nn]!] (* _Harvey P. Dale_, Mar 07 2018 *)
%K A009254 sign,easy
%O A009254 0,5
%A A009254 _R. H. Hardin_
%E A009254 Extended with signs by _Olivier Gérard_, Mar 15 1997
%E A009254 Previous Mathematica program replaced by _Harvey P. Dale_, Mar 07 2018