OFFSET
0,2
PROG
(PARI) a(n, k=3) = if(k==0, 0^n, k*sum(j=0, n, binomial(3*n-3*j+k, j)/(3*n-3*j+k)*a(n-j, j)));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jun 04 2025
STATUS
approved
