OFFSET
0,5
FORMULA
E.g.f.: exp( Sum_{n>=0} a(n) * x^(3*n+1) / (3*n+1)! ).
MATHEMATICA
a[0] = 1; a[n_] := a[n] = Sum[Binomial[n - 1, 3 k] a[k] a[n - 3 k - 1], {k, 0, Floor[(n - 1)/3]}]; Table[a[n], {n, 0, 27}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Feb 26 2022
STATUS
approved