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 A348876 #9 Nov 03 2021 04:40:49
%S A348876 1,2,10,122,3778,321794,79518154,58289895290,127713856067074,
%T A348876 838441945709583746,16506407616569722560778,
%U A348876 974752895709158578160969978,172678450359956040815290930278850,91769099059347441553324620759011469698,146309952397373808216450794120154608358754762
%N A348876 G.f. A(x) satisfies: A(x) = 1 / (1 - x - x * A(3*x)).
%F A348876 a(0) = 1; a(n) = a(n-1) + Sum_{k=0..n-1} 3^k * a(k) * a(n-k-1).
%F A348876 a(n) ~ c * 3^(n*(n-1)/2), where c = 2*Product_{j>=1} (3^j+1)/(3^j-1) = QPochhammer(-1, 1/3) / QPochhammer(1/3) = 5.58779203552209791475992929265... - _Vaclav Kotesovec_, Nov 03 2021
%t A348876 nmax = 14; A[_] = 0; Do[A[x_] = 1/(1 - x - x A[3 x]) + O[x]^(nmax + 1) // Normal, nmax + 1]; CoefficientList[A[x], x]
%t A348876 a[0] = 1; a[n_] := a[n] = a[n - 1] + Sum[3^k a[k] a[n - k - 1], {k, 0, n - 1}]; Table[a[n], {n, 0, 14}]
%Y A348876 Cf. A006318, A015084, A348875, A348877.
%K A348876 nonn
%O A348876 0,2
%A A348876 _Ilya Gutkovskiy_, Nov 02 2021