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A117907
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Expansion of x + (1-x)^2/(1-x^6).
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2
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1, -1, 1, 0, 0, 0, 1, -2, 1, 0, 0, 0, 1, -2, 1, 0, 0, 0, 1, -2, 1, 0, 0, 0, 1, -2, 1, 0, 0, 0, 1, -2, 1, 0, 0, 0, 1, -2, 1, 0, 0, 0, 1, -2, 1, 0, 0, 0, 1, -2, 1, 0, 0, 0, 1, -2, 1, 0, 0, 0, 1, -2, 1
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OFFSET
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0,8
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COMMENTS
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LINKS
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FORMULA
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G.f.: (1 +x^2 +x^3 +x^4 +x^5 +x^6)/(1 +x +x^2 +x^3 +x^4 +x^5).
a(n) = floor((5*n-1)/3) mod 2 - 3*[(n mod 6) = 1], n >= 2, with a(0) = 1, a(1) = -1. - G. C. Greubel, Oct 20 2021
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MATHEMATICA
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CoefficientList[Series[x+(1-x)^2/(1-x^6), {x, 0, 90}], x]
Join[{1, -1}, LinearRecurrence[{-1, -1, -1, -1, -1}, {1, 0, 0, 0, 1}, 90]]
PadRight[{1, -1}, 90, {1, -2, 1, 0, 0, 0}] (* End *)
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PROG
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(Magma) R<x>:=PowerSeriesRing(Integers(), 90); Coefficients(R!( x + (1-x)^2/(1-x^6) )); // G. C. Greubel, Oct 20 2021
(Sage)
def A117907(n): return (-1)^n if (n<2) else (((5*n-1)//3)%2) - 3*bool(n%6==1)
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CROSSREFS
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KEYWORD
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easy,sign
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AUTHOR
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STATUS
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approved
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