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 A009838 #25 Nov 28 2014 22:23:07
%S A009838 0,1,-2,4,-16,96,-576,3760,-30080,278656,-2786560,30298368,-363580416,
%T A009838 4748913664,-66484791296,995368112128,-15925889794048,270949991841792,
%U A009838 -4877099853152256,92635808324780032,-1852716166495600640
%N A009838 Expansion of e.g.f.: tanh(x)/(1+x).
%C A009838 Unsigned sequence satisfies a(n)=na(n-1)+b(n-1) where b(n) is defined in A009006. E.g.f. tanh(z)/(1-z). - Mario Catalani (mario.catalani(AT)unito.it), Feb 10 2003
%H A009838 Vincenzo Librandi, <a href="/A009838/b009838.txt">Table of n, a(n) for n = 0..200</a>
%F A009838 |a(n)| ~ n! * tanh(1). - _Vaclav Kotesovec_, Sep 22 2013
%p A009838 G(x):= tanh(x)/(1+x): f[0]:=G(x): for n from 1 to 21 do f[n]:=diff(f[n-1],x) od: x:=0: seq(f[n],n=0..20); # _Zerinvary Lajos_, Apr 03 2009
%t A009838 With[{nn=20},CoefficientList[Series[Tanh[x]/(1+x),{x,0,nn}],x] Range[ 0,nn]!] (* _Harvey P. Dale_, Jul 18 2013 *)
%K A009838 sign,easy
%O A009838 0,3
%A A009838 _R. H. Hardin_
%E A009838 Extended with signs by _Olivier Gérard_, Mar 15 1997
%E A009838 Prior Mathematica program replaced and definition clarified by _Harvey P. Dale_, Jul 18 2013