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 A013518 #27 Nov 12 2016 12:21:07
%S A013518 1,1,3,83,8887,57539,2419601,298733192941,84896691713,54207578317691,
%T A013518 535009143553922969,303988210353762448529,39439620915967757710853,
%U A013518 18146112662693896499335287481
%N A013518 Numerator of [x^(2n+1)] in the Taylor expansion arcsin(cosec(x)-cot(x)) = x/2 + x^3/16 + 3*x^5/256 + 83*x^7/30720 + 8887*x^9/12386304 + ...
%C A013518 The e.g.f. of x/2, arcsin(cosec(x)-cot(x)) = x/(2^1*1!) + 3*x^3/(2^3*3!) + 45*x^5/(2^5*5!) +1743*x^7(/2^7*7!) + 133305*x^9/(2^9*9!) + ..., is apparently covered by A012780.
%H A013518 G. C. Greubel, <a href="/A013518/b013518.txt">Table of n, a(n) for n = 0..216</a>
%F A013518 a(n)=(sum(k=0..n, (binomial(2*k,k)*sum(j=0..2*n-2*k, binomial(j+2*k,2*k)*(j+2*k+1)!*2^(-4*k-j-1)*(-1)^(n+k+j)*stirling2(2*n+1,j+2*k+1)))/(2*k+1)))/(2*n+1)!. - _Vladimir Kruchinin_, May 31 2013
%t A013518 Numerator[Take[CoefficientList[Series[ArcSin[Csc[x]-Cot[x]],{x,0,30}], x],{2,-1,2}]] (* _Harvey P. Dale_, Feb 02 2012 *)
%o A013518 (Maxima) a(n):=(sum((binomial(2*k,k)*sum(binomial(j+2*k,2*k)*(j+2*k+1)!*2^(-4*k-j-1)*(-1)^(n+k+j)*stirling2(2*n+1,j+2*k+1),j,0,2*n-2*k))/(2*k+1),k,0,n))/(2*n+1)!; /* _Vladimir Kruchinin_, May 31 2013 */
%Y A013518 Cf. A089171.
%K A013518 nonn,frac
%O A013518 0,3
%A A013518 Patrick Demichel (patrick.demichel(AT)hp.com)
%E A013518 Name edited by _R. J. Mathar_, Dec 19 2011