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 A102075 #7 Nov 05 2020 13:52:07
%S A102075 1,1,13,445,28985,3061625,476598725,102580436725,29164947696625,
%T A102075 10583881430448625,4773158983014768125,2618414864448579438125,
%U A102075 1716782830141547577475625,1325775140076807694645515625
%N A102075 Expansion of sec(arctanh(x)).
%e A102075 sec(arctanh(x)) = 1 + x^2/2 + 13x^4/4! + 445x^6/6! + 28985x^8/8! +...
%e A102075 sech(arctan(x)) = 1 - x^2/2 + 13x^4/4! - 445x^6/6! + 28985x^8/8! -...
%t A102075 With[{nn=30},Take[CoefficientList[Series[Sec[ArcTanh[x]],{x,0,nn}],x] Range[ 0,nn]!,{1,-1,2}]] (* _Harvey P. Dale_, Nov 05 2020 *)
%K A102075 nonn
%O A102075 0,3
%A A102075 _Ralf Stephan_, Dec 31 2004