%I #7 Aug 01 2021 03:49:23
%S 1,1,1,1,3,6,10,21,48,103,219,489,1114,2517,5712,13152,30492,70812,
%T 165165,387456,912378,2154250,5102343,12123027,28878384,68947041,
%U 164979006,395604531,950428335,2287387152,5514240673,13314167718,32194109193,77953239507,188997294360
%N G.f. A(x) satisfies: A(x) = 1 + x + x^2 + x^3 * A(x)^3.
%F a(0) = a(1) = a(2) = 1; a(n) = Sum_{i=0..n-3} Sum_{j=0..n-i-3} a(i) * a(j) * a(n-i-j-3).
%t nmax = 34; A[_] = 0; Do[A[x_] = 1 + x + x^2 + x^3 A[x]^3 + O[x]^(nmax + 1) // Normal, nmax + 1]; CoefficientList[A[x], x]
%t a[n_] := a[n] = If[n < 3, 1, Sum[Sum[a[i] a[j] a[n - i - j - 3], {j, 0, n - i - 3}], {i, 0, n - 3}]]; Table[a[n], {n, 0, 34}]
%Y Cf. A001764, A019497, A307970, A346734, A346735.
%K nonn
%O 0,5
%A _Ilya Gutkovskiy_, Jul 30 2021