OFFSET
0,3
FORMULA
a(0) = 1; a(n) = (n-1)! * Sum_{k=0..n-1} (k+1) * a(floor(k/3)) * a(n-1-k) / (6^floor(k/3) * floor(k/3)! * (n-1-k)!).
PROG
(PARI) a_vector(n) = my(v=vector(n+1)); v[1]=1; for(i=1, n, v[i+1]=(i-1)!*sum(j=0, i-1, (j+1)*v[j\3+1]*v[i-j]/(6^(j\3)*(j\3)!*(i-1-j)!))); v;
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Nov 29 2023
STATUS
approved