OFFSET
0,3
FORMULA
a(n) = n! * Sum_{k=0..floor(n/2)} (2*k+1)^(n-2*k-1) * binomial(3*k,k)/(n-2*k)!.
PROG
(PARI) a(n) = n!*sum(k=0, n\2, (2*k+1)^(n-2*k-1)*binomial(3*k, k)/(n-2*k)!);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Mar 18 2024
STATUS
approved