OFFSET
0,3
FORMULA
a(n) = Sum_{k=0..n} (-9)^k * binomial(-2*(n-k)/3,k) = Sum_{k=0..n} 9^(n-k) * binomial(n-k/3-1,n-k).
PROG
(PARI) my(N=30, x='x+O('x^N)); Vec(1/(1-x/(1-9*x)^(2/3)))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Apr 11 2023
STATUS
approved