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A373336
Expansion of Sum_{k>=1} x^k / (1 + x^k + x^(2*k) + x^(3*k) + x^(4*k) + x^(5*k) + x^(6*k)).
2
1, 0, 1, 0, 1, 0, 1, 1, 0, 0, 1, 0, 1, 0, 2, 0, 1, -1, 1, 0, 1, 1, 0, 1, 1, 0, 0, 0, 2, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 1, 1, 0, 2, 0, 1, -1, 1, 0, 1, 1, 0, 0, 1, -1, 1, 1, 2, 0, 1, 0, 1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 2, 0, 1, -1, 2, 0, 1, 1, 0, 0, 0, 0, 1, 0, 2, 0, 2, 1, 1, -1, 1, 0, 0, 0, 1, 0, 1, 0, 1, 0, 1, -1, 1, 1, 2
OFFSET
1,15
LINKS
FORMULA
G.f.: Sum_{k>=1} x^k * (1 - x^k) / (1 - x^(7*k)).
a(n) = A279061(n) - A363795(n).
PROG
(PARI) my(N=110, x='x+O('x^N)); Vec(sum(k=1, N, x^k*(1-x^k)/(1-x^(7*k))))
(PARI) a(n) = sumdiv(n, d, (d%7==1)-(d%7==2));
CROSSREFS
KEYWORD
sign,easy
AUTHOR
Seiichi Manyama, Jun 01 2024
STATUS
approved