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 A296842 #4 Dec 21 2017 16:02:10
%S A296842 1,0,-3,-15,-14,1755,60357,1740284,45816165,776485557,-37342503290,
%T A296842 -7203185712261,-822818831400759,-85463040449605000,
%U A296842 -8640073895507612019,-843669753827174738535,-73050419139737972150438,-3478007209663880122501701
%N A296842 Expansion of e.g.f. cos(x*tan(x/2)) (even powers only).
%F A296842 a(n) = (2*n)! * [x^(2*n)] cos(x*tan(x/2)).
%e A296842 cos(x*tan(x/2)) = 1 - 3*x^4/4! - 15*x^6/6! - 14*x^8/8! + 1755*x^10/10! + 60357*x^12/12! + ...
%t A296842 nmax = 17; Table[(CoefficientList[Series[Cos[x Tan[x/2]], {x, 0, 2 nmax}], x] Range[0, 2 nmax]!)[[n]], {n, 1, 2 nmax + 1, 2}]
%Y A296842 Cf. A001469, A003710, A009080, A110501, A296839, A296841.
%K A296842 sign
%O A296842 0,3
%A A296842 _Ilya Gutkovskiy_, Dec 21 2017