OFFSET
0,3
FORMULA
a(n) = n * Sum_{k=1..n-1} 3^k * (k-1)! * Stirling2(n-1,k).
PROG
(PARI) a(n) = n*sum(k=1, n-1, 3^k*(k-1)!*stirling(n-1, k, 2));
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Nov 19 2023
STATUS
approved