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A098018
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a(n) = Sum_{k|n, k>=2} mu(k-1), where mu() is the Moebius function.
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6
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0, 1, -1, 0, 0, -1, 1, -1, -1, 1, 1, -3, 0, 1, 0, 0, 0, -2, 0, -1, 0, 3, 1, -5, 0, 1, 0, 0, 0, -1, -1, -1, 0, 2, 2, -3, 0, 0, 0, -1, 0, -2, -1, 1, 0, 2, 1, -5, 1, 1, -1, 1, 0, -2, 1, 0, -1, 2, 1, -5, 0, -1, 1, -1, 0, 2, -1, 0, 0, 3, -1, -6, 0, 0, 1, -1, 2, 1, -1, -1, 0, 1, 1, -5, 0, 1, 0, 1, 0, -3, 1, 2, -2, 3, 1, -5, 0, 0, 0, -1, 0, -1, -1, -1, 2
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OFFSET
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1,12
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LINKS
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EXAMPLE
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12's divisors >=2 are 2, 3, 4, 6 and 12. So a(12) = mu(1) + mu(2) + mu(3) + mu(5) + mu(11) = 1 - 1 - 1 - 1 - 1 = -3.
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MATHEMATICA
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f[n_] := Plus @@ MoebiusMu[ Drop[ Divisors[n], 1] - 1]; Table[ f[n], {n, 105}] (* Robert G. Wilson v, Nov 01 2004 *)
Table[DivisorSum[n, MoebiusMu[# - 1] &, # > 1 &], {n, 105}] (* Michael De Vlieger, Sep 04 2017 *)
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PROG
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CROSSREFS
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KEYWORD
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sign
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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