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A369874
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a(n) is the constant term in the expansion of Product_{d|n} (x^d + 1 + 1/x^d).
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2
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1, 1, 1, 1, 1, 5, 1, 1, 1, 1, 1, 23, 1, 1, 1, 1, 1, 13, 1, 13, 1, 1, 1, 103, 1, 1, 1, 7, 1, 77, 1, 1, 1, 1, 1, 175, 1, 1, 1, 63, 1, 49, 1, 1, 5, 1, 1, 463, 1, 1, 1, 1, 1, 41, 1, 39, 1, 1, 1, 2975, 1, 1, 3, 1, 1, 33, 1, 1, 1, 25, 1, 2363, 1, 1, 1, 1, 1, 25, 1, 261
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OFFSET
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1,6
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COMMENTS
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a(n) is the number of solutions to 0 = Sum_{d|n} c_i * d with c_i in {-1,0,1}, i=1..tau(n), tau = A000005.
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LINKS
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MATHEMATICA
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Table[Coefficient[Product[(x^d + 1 + 1/x^d), {d, Divisors[n]}], x, 0], {n, 1, 80}]
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PROG
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(Python)
from collections import Counter
from sympy import divisors
c = {0:1}
for d in divisors(n, generator=True):
b = Counter(c)
for j in c:
a = c[j]
b[j+d] += a
b[j-d] += a
c = b
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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