OFFSET
0,2
FORMULA
a(n) = 9^n * Sum_{k>=0} (1/2)^(k+1) * binomial(n-1+2*k/3,n).
PROG
(PARI) my(N=20, x='x+O('x^N)); Vec(1/(2-1/(1-9*x)^(2/3)))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Aug 04 2024
STATUS
approved