OFFSET
0,3
FORMULA
a(n) = n! * Sum_{k=0..n-1} (k+1)^(n-k-1) * binomial(n+3*k,k)/((n+3*k) * (n-k-1)!) for n > 0.
PROG
(PARI) a(n) = if(n==0, 1, n!*sum(k=0, n-1, (k+1)^(n-k-1)*binomial(n+3*k, k)/((n+3*k)*(n-k-1)!)));
CROSSREFS
KEYWORD
nonn,new
AUTHOR
Seiichi Manyama, Mar 12 2025
STATUS
approved