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 A385346 #12 Jun 27 2025 05:45:34
%S A385346 1,2,8,50,416,4338,54272,792402,13221888,248206818,5177131008,
%T A385346 118784695218,2973171646464,80619877999698,2354230063005696,
%U A385346 73657841729314002,2458203242895507456,87165684035402711490,3272629788196529504256,129696816160868956695090
%N A385346 Expansion of e.g.f. 1/(1 - 2 * arcsin(x)).
%F A385346 a(n) = Sum_{k=0..n} 2^k * k! * A385343(n,k).
%F A385346 a(n) ~ sqrt(Pi/2) * cos(1/2) * n^(n + 1/2) / (exp(n) * sin(1/2)^(n+1)). - _Vaclav Kotesovec_, Jun 27 2025
%o A385346 (PARI) my(N=20, x='x+O('x^N)); Vec(serlaplace(1/(1-2*asin(x))))
%Y A385346 Cf. A189780, A385347.
%Y A385346 Cf. A385343.
%K A385346 nonn,easy
%O A385346 0,2
%A A385346 _Seiichi Manyama_, Jun 26 2025