OFFSET
0,3
FORMULA
a(n) = Sum_{k=1..n} (3*k)^(n-k) * (k-1)! * binomial(n,k).
a(n) ~ (n-1)! * 3^n / LambertW(3)^n. - Vaclav Kotesovec, Mar 11 2024
MATHEMATICA
With[{nn=20}, CoefficientList[Series[-Log[1-x Exp[3x]], {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, Mar 10 2024 *)
PROG
(PARI) a(n) = sum(k=1, n, (3*k)^(n-k)*(k-1)!*binomial(n, k));
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Dec 14 2023
STATUS
approved