OFFSET
0,3
FORMULA
G.f.: Sum_{k>=0} x^k/(1 - (3^k - 1)*x)^(k+1).
a(n) = Sum_{k=0..n} (3^k - 1)^(n-k) * binomial(n,k).
PROG
(PARI) my(N=20, x='x+O('x^N)); Vec(serlaplace(1+sum(k=1, N, exp((3^k-1)*x)*x^k/k!)))
(PARI) my(N=20, x='x+O('x^N)); Vec(sum(k=0, N, x^k/(1-(3^k-1)*x)^(k+1)))
(PARI) a(n) = sum(k=0, n, (3^k-1)^(n-k)*binomial(n, k));
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Feb 26 2023
STATUS
approved