OFFSET
0,2
FORMULA
a(n) = (1/(n+1)) * Sum_{k=0..n} 9^k * binomial(n/3+1/3,k) * binomial(k,n-k).
a(3*n+2) = 0 for n > 0.
a(n) = 9^n*binomial((n+1)/3, n)*hypergeom([(1-n)/2, -n/2], [2*(2-n)/3], 4/9)/(n+1). - Stefano Spezia, Apr 18 2024
D-finite with recurrence n*(n-1)*(2*n-11)*a(n) -108*(n-5)*(n-3)^2*a(n-3) -135*(n-5)*(n-8)*(2*n-5)*a(n-6)=0. - R. J. Mathar, Apr 22 2024
MAPLE
A372004 := proc(n)
add(9^k*binomial((n+1)/3, k)*binomial(k, n-k), k=0..n)/(n+1) ;
end proc:
seq(A372004(n), n=0..60) ; # R. J. Mathar, Apr 22 2024
PROG
(PARI) a(n) = sum(k=0, n, 9^k*binomial(n/3+1/3, k)*binomial(k, n-k))/(n+1);
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Apr 15 2024
STATUS
approved