OFFSET
0,3
FORMULA
a(n) = -Sum_{k=0..n} (-9)^k * binomial((n-k)/3,k).
PROG
(PARI) my(N=30, x='x+O('x^N)); Vec(-1/(1-x*(1-9*x)^(1/3)))
CROSSREFS
KEYWORD
sign,easy
AUTHOR
Seiichi Manyama, Apr 09 2023
STATUS
approved