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 A024257 #9 Apr 02 2017 15:31:07
%S A024257 0,1,4,-72,-5632,-161920,18173952,4194147328,310213328896,
%T A024257 -84365860995072,-39813939519815680,-5549928926785306624,
%U A024257 2813587774502929956864,2234702652489178135134208,497733049858403607865458688
%N A024257 Expansion of tanh(tan(x)*x)/2.
%t A024257 With[{nn=30},Take[CoefficientList[Series[Tanh[Tan[x]*x]/2 ,{x,0,nn}],x] Range[0,nn]!,{1,-1,2}]] (* _Harvey P. Dale_, Apr 27 2016 *)
%Y A024257 Cf. A009817.
%K A024257 sign
%O A024257 0,3
%A A024257 _R. H. Hardin_
%E A024257 Extended with signs Mar 1997
%E A024257 Prior Mathematica program deleted by _Harvey P. Dale_, Apr 27 2016