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 A302542 #5 Apr 09 2018 22:33:54
%S A302542 1,1,29,-139,31737,-1824151,313750293,-51584719523,13137192234225,
%T A302542 -3947317975733039,1522475446731094285,-702509124781480897211,
%U A302542 389722900767594460770025,-253710144786166583863030983,192285396891961478711402819077,-167564604997707653568802119363795
%N A302542 Expansion of e.g.f. arctan(x)/cos(x) (odd powers only).
%F A302542 a(n) = (2*n+1)! * [x^(2*n+1)] arctan(x)/cos(x).
%e A302542 arctan(x)/cos(x) = x/1! + x^3/3! + 29*x^5/5! - 139*x^7/7! + 31737*x^9/9! - 1824151*x^11/11! + ...
%t A302542 nmax = 16; Table[(CoefficientList[Series[ArcTan[x]/Cos[x], {x, 0, 2 nmax + 1}], x] Range[0, 2 nmax + 1]!)[[n]], {n, 2, 2 nmax, 2}]
%Y A302542 Cf. A000182, A000364, A000795, A002084, A003701, A003702, A010050, A012801, A191003, A301942, A302444, A302543.
%K A302542 sign
%O A302542 0,3
%A A302542 _Ilya Gutkovskiy_, Apr 09 2018