OFFSET
0,4
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..549
FORMULA
a(n) = Sum_{k=0..floor(n/2)} 3^(n-2*k) * Stirling2(n-k,k).
MATHEMATICA
a[n_] := Sum[3^(n-2*k) * StirlingS2[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^(2*k)/prod(j=1, k, 1-3*j*x)))
(PARI) a(n) = sum(k=0, n\2, 3^(n-2*k)*stirling(n-k, k, 2));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Apr 09 2022
STATUS
approved