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 A003718 M3694 #35 Jan 27 2018 18:20:11
%S A003718 1,4,72,2896,203904,22112000,3412366336,709998153728,191483931951104,
%T A003718 64956739430973440,27065724289967718400,13588059904833174896640,
%U A003718 8089418253144660155301888,5634743143901240164716904448,4539998748622480932947483426816
%N A003718 E.g.f. tan(tan(x)), zeros omitted.
%D A003718 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A003718 T. D. Noe, <a href="/A003718/b003718.txt">Table of n, a(n) for n = 0..50</a>
%F A003718 a(n) ~ 8 * (2*n+1)! / ((4+Pi^2) * (arctan(Pi/2))^(2*n+2)). - _Vaclav Kotesovec_, Feb 16 2015
%t A003718 Rest@ Union[ Range[0, 29]! CoefficientList[ Series[ Tan@ Tan@ x, {x, 0, 29}], x]] (* _Robert G. Wilson v_, May 07 2011 *)
%o A003718 (Maxima)
%o A003718 a(n):=b(2*n+1);
%o A003718 b(n):=sum((((-1)^(k-1)+1)*(sum(j!*2^(k-j-1)*(-1)^((k+1)/2+j)* stirling2(k,j),j,1,k))*((-1)^(n-k)+1)*sum(binomial(j-1,k-1)*j!*2^(n-j-1)*(-1)^((n+k)/2+j)*stirling2(n,j),j,k,n))/k!,k,1,n); /* _Vladimir Kruchinin_, Apr 23 2011 */
%K A003718 nonn
%O A003718 0,2
%A A003718 _R. H. Hardin_
%E A003718 Extended and formatted by _Olivier Gérard_, Mar 15 1997
%E A003718 Name corrected by _Joerg Arndt_, Apr 23 2011