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 A009817 #28 Dec 23 2017 05:00:10
%S A009817 0,2,8,-144,-11264,-323840,36347904,8388294656,620426657792,
%T A009817 -168731721990144,-79627879039631360,-11099857853570613248,
%U A009817 5627175549005859913728,4469405304978356270268416
%N A009817 Expansion of e.g.f. tanh(tan(x)*x) (even powers only).
%H A009817 Iain Fox, <a href="/A009817/b009817.txt">Table of n, a(n) for n = 0..231</a> (first 101 terms from Vincenzo Librandi)
%p A009817 S:= series(tanh(tan(x)*x),x,41):
%p A009817 seq(coeff(S,x,n)*n!,n=0..40,2); # _Robert Israel_, Dec 21 2017
%t A009817 With[{nn=30},Take[CoefficientList[Series[Tanh[Tan[x]*x],{x,0,nn}],x] Range[0,nn]!,{1,-1,2}]] (* _Harvey P. Dale_, Oct 28 2013 *)
%o A009817 (PARI) first(n) = x='x+O('x^(2*n-1)); vecextract(Vec(serlaplace(tanh(tan(x)*x)), -2*n), (4^n - 1)/3) \\ _Iain Fox_, Dec 21 2017
%Y A009817 Cf. A000182, A003718, A009707, A024257.
%K A009817 sign
%O A009817 0,2
%A A009817 _R. H. Hardin_, Mar 15 1996
%E A009817 Extended with signs by _Olivier Gérard_, Mar 15 1997
%E A009817 Prior Mathematica program replaced by _Harvey P. Dale_, Oct 28 2013