OFFSET
0,2
FORMULA
a(n) = 9^n * Sum_{k=0..n} (-1)^k * binomial(1/3,k) * binomial(n-4*k/3-1,n-k).
PROG
(PARI) a(n) = 9^n*sum(k=0, n, (-1)^k*binomial(1/3, k)*binomial(n-4*k/3-1, n-k));
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Oct 21 2024
STATUS
approved