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 A012231 #6 Nov 28 2016 18:05:20
%S A012231 1,1,1,1,1,9,49,281,1345,13233,105441,1179729,10336833,144386553,
%T A012231 1580651409,25501409961,316289380737,5869292202465,83559601907649,
%U A012231 1744083324947745,27709107620492673,643531258862953065
%N A012231 exp(arctan(arctanh(x)))=1+x+1/2!*x^2+1/3!*x^3+1/4!*x^4+9/5!*x^5...
%t A012231 With[{nn=30},CoefficientList[Series[Exp[ArcTan[ArcTanh[x]]],{x,0,nn}],x] Range[0,nn]!] (* _Ray Chandler_, Nov 28 2016 *)
%K A012231 nonn
%O A012231 0,6
%A A012231 Patrick Demichel (patrick.demichel(AT)hp.com)