OFFSET
0,5
FORMULA
G.f.: Sum_{k>=0} x^k * Product_{j=0..k-1} (1 + j * x^2).
MATHEMATICA
Table[Sum[Abs[StirlingS1[n-2k, n-3k]], {k, 0, Floor[n/3]}], {n, 0, 40}] (* Harvey P. Dale, Nov 01 2023 *)
PROG
(PARI) a(n) = sum(k=0, n\3, abs(stirling(n-2*k, n-3*k, 1)));
(PARI) my(N=40, x='x+O('x^N)); Vec(sum(k=0, N, x^k*prod(j=0, k-1, 1+j*x^2)))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Oct 21 2022
STATUS
approved