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 A013519 #14 Nov 13 2016 06:55:00
%S A013519 1,1,3,181,59,3455,3332389,173339393,449509681,198232237033,
%T A013519 1032475444411,101635950910031,71432133543444211,671713726985602398481
%N A013519 Numerator of [x^(2n+1)] in the Taylor expansion tan(cosec(x)-cot(x)).
%C A013519 The e.g.f. of x/2, tan(cosec(x)-cot(x)) = x/(2^1*1!) + 4*x^3/(2^3*3!) +72*x^5/(2^5*5!) + 2896*x^7/(2^7*7!) +.. is apparently covered by A003718.
%H A013519 G. C. Greubel, <a href="/A013519/b013519.txt">Table of n, a(n) for n = 0..125</a>
%e A013519 x/2 +x^3/12 +3*x^5/160 +181*x^7/40320 +59*x^9/53760 +3455*x^11/12773376 +...
%t A013519 Numerator[Take[CoefficientList[Series[Tan[Csc[x] - Cot[x]], {x, 0, 25}], x], {2, -1, 2}]] (* _G. C. Greubel_, Nov 12 2016 *)
%K A013519 nonn,frac
%O A013519 0,3
%A A013519 Patrick Demichel (patric.demichel(AT)hp.com)
%E A013519 Name edited by _R. J. Mathar_, Dec 19 2011