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 A009723 #14 Nov 28 2024 03:31:54
%S A009723 1,3,57,1995,128881,12775059,1796958633,342118793307,84276974508769,
%T A009723 26141579246291235,9956883572644073241,4570240365824839488747,
%U A009723 2487549038143714062879313,1584207614996350912703688627
%N A009723 Expansion of tan(tanh(x)/cos(x)).
%F A009723 a(n) ~ c * d^n * n^(2*n + 3/2), where d = 0.491131788453837761770391039276... and c = 3.6558020994214430118438069889... - _Vaclav Kotesovec_, Nov 27 2024
%t A009723 With[{nn=30},Take[CoefficientList[Series[Tan[Tanh[x]/Cos[x]],{x,0,nn}],x] Range[0,nn-1]!,{2,-1,2}]] (* _Harvey P. Dale_, Dec 15 2014 *)
%K A009723 nonn
%O A009723 0,2
%A A009723 _R. H. Hardin_
%E A009723 Extended and signs tested Mar 15 1997 by _Olivier Gérard_.
%E A009723 Prior Mathematica program replaced by _Harvey P. Dale_, Dec 15 2014