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 A348904 #8 Nov 03 2021 15:42:50
%S A348904 1,4,24,224,3264,76544,3055104,220125184,29946753024,7906463105024,
%T A348904 4111398632914944,4242968041649209344,8723543411935886966784,
%U A348904 35801422714130756942168064,293571666811153273905871847424,4812226763497124503879315624034304,157725544404988739801460227609821446144
%N A348904 G.f. A(x) satisfies: A(x) = 1 / (1 - 3*x - x * A(2*x)).
%H A348904 Michael De Vlieger, <a href="/A348904/b348904.txt">Table of n, a(n) for n = 0..81</a>
%F A348904 a(n) ~ c * 2^(n*(n-1)/2), where c = 118.688483279581472418531869762515593107529867862298434268...
%F A348904 a(0) = 1; a(n) = 3 * a(n-1) + Sum_{k=0..n-1} 2^k * a(k) * a(n-k-1). - _Ilya Gutkovskiy_, Nov 03 2021
%t A348904 nmax = 20; A[_] = 0; Do[A[x_] = 1/(1 - 3*x - x*A[2*x]) + O[x]^(nmax + 1) // Normal, nmax + 1]; CoefficientList[A[x], x]
%Y A348904 Cf. A348903.
%K A348904 nonn
%O A348904 0,2
%A A348904 _Vaclav Kotesovec_, Nov 03 2021