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 A009707 #17 Dec 21 2017 17:37:07
%S A009707 0,2,8,336,15616,1450240,185032704,33566984192,7971973332992,
%T A009707 2424984197529600,915532582868746240,420569934453637906432,
%U A009707 230845747512083447021568,149228982402223336708898816
%N A009707 Expansion of e.g.f. tan(tan(x)*x) (even powers only).
%H A009707 Vaclav Kotesovec, <a href="/A009707/b009707.txt">Table of n, a(n) for n = 0..200</a>
%F A009707 a(n) ~ c * d^n * n^(2*n + 1/2) / exp(2*n), where d = 3.9786913954409425781217887822690623430980810... is the root of the equation tan(2/sqrt(d)) = Pi*sqrt(d)/4 and c = 1.4057183994645... - _Vaclav Kotesovec_, Dec 21 2017
%t A009707 nmax = 20; Table[(CoefficientList[Series[Tan[x*Tan[x]], {x, 0, 2*nmax}], x] * Range[0, 2 nmax]!)[[n]], {n, 1, 2*nmax + 1, 2}] (* _Vaclav Kotesovec_, Dec 21 2017 *)
%Y A009707 Cf. A000182, A003718, A009752, A024265.
%K A009707 nonn
%O A009707 0,2
%A A009707 _R. H. Hardin_
%E A009707 Extended and signs tested Mar 15 1997 by _Olivier Gérard_.