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 A296787 #7 Dec 21 2017 06:24:18
%S A296787 1,2,4,24,-496,36000,-3753408,556961664,-111591202560,29054584410624,
%T A296787 -9541382573767680,3858875286730168320,-1884995591107521540096,
%U A296787 1094305223336273239449600,-744771228363250138965196800,587358379156469629707528929280
%N A296787 Expansion of e.g.f. exp(x*arctan(x)) (even powers only).
%F A296787 a(n) = (2*n)! * [x^(2*n)] exp(x*arctan(x)).
%F A296787 a(n) ~ -(-1)^n * 2^(2*n-1) * n^(2*n-1) / exp(2*n). - _Vaclav Kotesovec_, Dec 21 2017
%e A296787 exp(x*arctan(x)) = 1 + 2*x^2/2! + 4*x^4/4! + 24*x^6/6! - 496*x^8/8! + ...
%t A296787 nmax = 15; Table[(CoefficientList[Series[Exp[x ArcTan[x]], {x, 0, 2 nmax}], x] Range[0, 2 nmax]!)[[n]], {n, 1, 2 nmax + 1, 2}]
%t A296787 nmax = 15; Table[(CoefficientList[Series[Exp[(I/2) x (Log[1 - I x] - Log[1 + I x])], {x, 0, 2 nmax}], x] Range[0, 2 nmax]!)[[n]], {n, 1, 2 nmax + 1, 2}]
%Y A296787 Cf. A002019, A009252, A009273, A010050, A102059, A166356, A259647, A293192, A296788, A296789.
%K A296787 sign
%O A296787 0,2
%A A296787 _Ilya Gutkovskiy_, Dec 20 2017