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 A367939 #9 Dec 07 2023 08:23:21
%S A367939 1,2,20,168,1936,25376,378688,6284928,114471168,2263605760,
%T A367939 48192279552,1097180784640,26562251100160,680591327567872,
%U A367939 18381995707154432,521521320660205568,15495495061984051200,480873815489757970432,15549555768325162926080,522810678067316117733376
%N A367939 Expansion of e.g.f. exp(exp(4*x) - 1 - 2*x).
%F A367939 G.f. A(x) satisfies: A(x) = 1 - 2 * x * ( A(x) - 2 * A(x/(1 - 4*x)) / (1 - 4*x) ).
%F A367939 a(n) = exp(-1) * Sum_{k>=0} (4*k-2)^n / k!.
%F A367939 a(0) = 1; a(n) = -2 * a(n-1) + Sum_{k=1..n} binomial(n-1,k-1) * 4^k * a(n-k).
%F A367939 a(n) = Sum_{k=0..n} binomial(n,k) * (-2)^(n+k) * Bell(k).
%F A367939 a(n) = 2^n * |A124311(n)|.
%t A367939 nmax = 19; CoefficientList[Series[Exp[Exp[4 x] - 1 - 2 x], {x, 0, nmax}], x] Range[0, nmax]!
%t A367939 a[0] = 1; a[n_] := a[n] = -2 a[n - 1] + Sum[Binomial[n - 1, k - 1] 4^k a[n - k], {k, 1, n}]; Table[a[n], {n, 0, 19}]
%t A367939 Table[Sum[Binomial[n, k] (-2)^(n + k) BellB[k], {k, 0, n}], {n, 0, 19}]
%o A367939 (PARI) my(x='x+O('x^30)); Vec(serlaplace(exp(exp(4*x) - 1 - 2*x))) \\ _Michel Marcus_, Dec 07 2023
%Y A367939 Cf. A000110, A124311, A126617, A355162, A367786, A367938, A367940.
%K A367939 nonn
%O A367939 0,2
%A A367939 _Ilya Gutkovskiy_, Dec 05 2023