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 A296741 #9 Dec 19 2017 16:22:44
%S A296741 1,4,64,2752,237312,34390016,7512117248,2302977392640,942529341030400,
%T A296741 496287845973753856,326775812392982937600,263039306566659448242176,
%U A296741 254121613033387345942937600,290175686081926976733941071872,386599796043915196967089006968832
%N A296741 Expansion of e.g.f. arcsin(x*sec(x)) (odd powers only).
%F A296741 a(n) = (2*n+1)! * [x^(2*n+1)] arcsin(x*sec(x)).
%e A296741 arcsin(x*sec(x)) = x/1! + 4*x^3/3! + 64*x^5/5! + 2752*x^7/7! + 237312*x^9/9! + ...
%t A296741 nmax = 15; Table[(CoefficientList[Series[ArcSin[x Sec[x]], {x, 0, 2 nmax + 1}], x] Range[0, 2 nmax + 1]!)[[n]], {n, 2, 2 nmax, 2}]
%o A296741 (PARI) first(n) = x='x+O('x^(2*n)); vecextract(Vec(serlaplace(asin(x/cos(x)))), (4^n - 1)/3) \\ _Iain Fox_, Dec 19 2017
%Y A296741 Cf. A001818, A003700, A009118, A009119, A009562, A009563, A009765, A009843, A102072, A191003, A296464, A296466, A296679, A296680, A296742, A296743.
%K A296741 nonn
%O A296741 0,2
%A A296741 _Ilya Gutkovskiy_, Dec 19 2017