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 A012227 #7 Dec 08 2018 19:37:13
%S A012227 1,-6,176,-12016,1469696,-280971776,77198422016,-28793654081536,
%T A012227 13988424620507136,-8578076577450295296,6478101995566379565056,
%U A012227 -5906079803365219349037056,6394716233788355978540875776
%N A012227 tanh(arctan(tanh(x)))=x-6/3!*x^3+176/5!*x^5-12016/7!*x^7...
%t A012227 With[{nn=30},Take[CoefficientList[Series[Tanh[ArcTan[Tanh[x]]],{x,0,nn}],x] Range[0,nn-1]!,{2,-1,2}]] (* _Harvey P. Dale_, Dec 08 2018 *)
%Y A012227 Cf. A101921.
%K A012227 sign
%O A012227 0,2
%A A012227 Patrick Demichel (patrick.demichel(AT)hp.com)