OFFSET
0,3
FORMULA
a(n) = n! * (3*n)! * Sum_{k=0..floor(n/2)} |Stirling1(n-k,k)|/( (n-k)! * (3*n-k+1)! ).
PROG
(PARI) a(n) = n!*(3*n)!*sum(k=0, n\2, abs(stirling(n-k, k, 1))/((n-k)!*(3*n-k+1)!));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Mar 15 2024
STATUS
approved