OFFSET
0,3
COMMENTS
Alternating row sums of A291451.
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..205
MAPLE
A291974 := proc(n) exp(-(exp(z)/3+2*exp(-z/2)*cos(z*sqrt(3)/2)/3-1)):
(3*n)!*coeff(series(%, z, 3*(n+1)), z, 3*n) end:
seq(A291974(n), n=0..15);
# second Maple program:
b:= proc(n, t) option remember; `if`(n=0, 1-2*t, add(
b(n-3*j, 1-t)*binomial(n-1, 3*j-1), j=1..n/3))
end:
a:= n-> b(3*n, 0):
seq(a(n), n=0..20); # Alois P. Heinz, Aug 14 2019
MATHEMATICA
b[n_, t_] := b[n, t] = If[n == 0, 1-2t, Sum[b[n-3j, 1-t] * Binomial[n-1, 3j-1], {j, 1, n/3}]];
a[n_] := b[3n, 0];
Table[a[n], {n, 0, 20}] (* Jean-François Alcover, Jan 27 2023, after Alois P. Heinz *)
CROSSREFS
KEYWORD
sign
AUTHOR
Peter Luschny, Sep 07 2017
STATUS
approved