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 A013525 #16 Nov 13 2016 06:20:44
%S A013525 1,0,2,30,692,25260,1351382,99680490,9695756072,1202439837720,
%T A013525 185185594118762,34674437196568950,7757267081778543452,
%U A013525 2043536254646561946180,626129820701814932734142,220771946624511552276841410
%N A013525 E.g.f.: x + (gdinv x - sinh x)/2, where gdinv = inverse-Gudermannian. Sequence has odd-indexed coefficients; others are zero.
%C A013525 Also gdinv(x) = log(tan(x) + sec(x)).
%H A013525 G. C. Greubel, <a href="/A013525/b013525.txt">Table of n, a(n) for n = 0..200</a>
%F A013525 For n>0, a(n) = (1/2) * (A000364(n) - 1).
%e A013525 x + (gdinv x - sinh x)/2 = x + 2/5!*x^5 + 30/7!*x^7 + 692/9!*x^9 + ...
%t A013525 With[{nn=40},Take[CoefficientList[Series[x+(InverseGudermannian[x]-Sinh[ x])/2,{x,0,nn}],x] Range[0,nn-1]!,{2,-1,2}]] (* _Harvey P. Dale_, Oct 16 2014 *)
%K A013525 nonn,easy
%O A013525 0,3
%A A013525 Patrick Demichel (patrick.demichel(AT)hp.com)
%E A013525 Definition corrected by _Ralf Stephan_ and _Don Reble_, Dec 16 2004