OFFSET
0,2
FORMULA
a(n) = (1/(n+1)) * Sum_{k=0..n} (3*n-k+2)^k * (2*n-k)!/(k! * (n-k)!).
PROG
(PARI) a(n) = sum(k=0, n, (3*n-k+2)^k*(2*n-k)!/(k!*(n-k)!))/(n+1);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Dec 29 2024
STATUS
approved