OFFSET
0,5
FORMULA
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).
MATHEMATICA
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]
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}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Jul 30 2021
STATUS
approved