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A321436
Expansion of Product_{1 <= i <= j} (1 - x^(i^2 + j^2)).
5
1, 0, -1, 0, 0, -1, 0, 1, -1, 0, 0, 0, 1, 0, 0, 1, 0, -2, 1, 1, -2, 1, 2, 0, -1, 0, -1, 0, 2, -2, 1, 1, -4, 0, 3, -1, -1, 3, -2, -1, 0, -4, 5, 2, -3, 2, 3, -5, -3, 6, -3, -1, 0, -2, 1, 1, 0, 2, 7, -7, 0, 7, -9, -2, 4, -3, 2, 6, -9, 2, 12, -12, 1, 9, -11, -3, 7, 0, -1, 5
OFFSET
0,18
LINKS
FORMULA
G.f.: Product_{k>0} (1 - x^k)^A025426(k).
MAPLE
N:= 100: # for a(1)..a(N)
P:= 1:
for i from 1 to floor(sqrt(N)) do
for j from i while i^2 + j^2 <= N do
P:= P * (1 - x^(i^2 + j^2))
od od:
S:= series(P, x, N+1):
seq(coeff(S, x, k), k=0..N): # Robert Israel, Apr 21 2024
CROSSREFS
KEYWORD
sign,look
AUTHOR
Seiichi Manyama, Nov 09 2018
STATUS
approved