OFFSET
0,2
FORMULA
See A381573.
PROG
(PARI) a(n, k=1) = if(k==0, 0^n, 3*k*sum(j=0, n, binomial(3*n-2*j+3*k, j)/(3*n-2*j+3*k)*a(n-j, j)));
CROSSREFS
KEYWORD
nonn,new
AUTHOR
Seiichi Manyama, Feb 28 2025
STATUS
approved