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 A013523 #19 Nov 13 2016 06:55:35
%S A013523 2,48,768,645120,37158912,81749606400,784796221440,42849873690624000,
%T A013523 548478383239987200,63777066403145711616000,4285818862291391820595200,
%U A013523 216862434431944426122117120000,8007228348256409579893555200000,1461479318123759876522171695104000000
%N A013523 Denominator of [x^(2n+1)] in the Taylor expansion arcsinh(cosec(x) - cot(x)).
%C A013523 Numerators are apparently covered by A091912.
%C A013523 The e.g.f. of x/2, arcsinh(cosec(x)-cot(x)) = x/(2^1*1!) + x^3/(2^3*3!) + 5*x^5/(2^5*5!) + 61*x^7/(2^7*7!) + 1385*x^9/(2^9*9!) + ... is apparently provided by the absolute values of A028296.
%H A013523 G. C. Greubel, <a href="/A013523/b013523.txt">Table of n, a(n) for n = 0..200</a>
%e A013523 x/2 + x^3/48 + x^5/768 + 61*x^7/645120 + 277*x^9/37158912 + ...
%t A013523 Denominator[Take[CoefficientList[Series[ArcSinh[Csc[x] - Cot[x]], {x,0,25}], x], {2, -1, 2}]] (* _G. C. Greubel_, Nov 12 2016 *)
%K A013523 nonn,frac
%O A013523 0,1
%A A013523 Patrick Demichel (patrick.demichel(AT)hp.com)
%E A013523 Name edited by _R. J. Mathar_, Dec 19 2011