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 A009518 #24 Dec 10 2024 05:41:05
%S A009518 0,2,16,152,-5504,-1107808,-155757824,-22741022848,-3557729644544,
%T A009518 -565165935635968,-73212906789515264,4150737348343519232,
%U A009518 11583034460298696687616,8797240254608561943191552
%N A009518 Expansion of e.g.f. sin(tan(x)^2) (even powers only).
%H A009518 Vincenzo Librandi, <a href="/A009518/b009518.txt">Table of n, a(n) for n = 0..100</a>
%F A009518 a(n) = sum(m=0..(n-1)/2, sum(j=4*m+2..2*n, binomial(j-1,4*m+1)*(j)!*2^(2*n-j)*(-1)^(n+m+j+1)*stirling2(2*n,j))/(2*m+1)!). - _Vladimir Kruchinin_, Jun 10 2011
%e A009518 sin(tan(x)*tan(x))=2/2!*x^2+16/4!*x^4+152/6!*x^6-5504/8!*x^8...
%t A009518 With[{nn=30},Take[CoefficientList[Series[Sin[Tan[x]^2],{x,0,nn}], x] Range[0,nn]!,{1,-1,2}]] (* _Harvey P. Dale_, May 17 2012 *)
%o A009518 (Maxima)
%o A009518 a(n):=sum(sum(binomial(j-1,4*m+1)*(j)!*2^(2*n-j)*(-1)^(n+m+j+1)*stirling2(2*n,j),j,4*m+2,2*n)/(2*m+1)!,m,0,(n-1)/2); /* _Vladimir Kruchinin_, Jun 10 2011 */
%K A009518 sign
%O A009518 0,2
%A A009518 _R. H. Hardin_
%E A009518 Extended with signs by _Olivier Gérard_, Mar 15 1997