OFFSET
0,3
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..451
FORMULA
a(n) = Sum_{k=0..floor(n/2)} 3^k * |Stirling1(n-k,k)|.
MATHEMATICA
a[n_] := Sum[3^k * Abs[StirlingS1[n - k, k]], {k, 0, Floor[n/2]}]; Array[a, 25, 0] (* Amiram Eldar, Apr 09 2022 *)
PROG
(PARI) my(N=40, x='x+O('x^N)); Vec(sum(k=0, N, x^k*prod(j=0, k-1, j+3*x)))
(PARI) a(n) = sum(k=0, n\2, 3^k*abs(stirling(n-k, k, 1)));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Apr 09 2022
STATUS
approved