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 A012222 #6 Mar 17 2025 16:51:25
%S A012222 1,1,1,-3,-15,41,561,-1243,-40415,58001,4825121,-1956083,-866056815,
%T A012222 -740509639,218527875281,509169335477,-73838559553215,
%U A012222 -295854887910879,32207514779999041,189240977761969437
%N A012222 Expansion of e.g.f.: exp(arctan(tanh(x)))=1+x+1/2!*x^2-3/3!*x^3-15/4!*x^4+41/5!*x^5...
%t A012222 With[{nn=20},CoefficientList[Series[Exp[ArcTan[Tanh[x]]],{x,0,nn}],x] Range[0,nn]!] (* _Harvey P. Dale_, Mar 17 2025 *)
%K A012222 sign
%O A012222 0,4
%A A012222 Patrick Demichel (patrick.demichel(AT)hp.com)
%E A012222 Definition clarified by _Harvey P. Dale_, Mar 17 2025