OFFSET
0,2
FORMULA
a(n) = Sum_{k=0..n} 9^k * binomial(4*k/3-2/3,k) * binomial(k,n-k)/(k+1).
PROG
(PARI) a(n) = sum(k=0, n, 9^k*binomial(4*k/3-2/3, k)*binomial(k, n-k)/(k+1));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Apr 17 2024
STATUS
approved