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 A098018 a(n) = Sum_{k|n, k>=2} mu(k-1), where mu() is the Moebius function. 6
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,12 LINKS Michael De Vlieger, Table of n, a(n) for n = 1..10000 EXAMPLE 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. MATHEMATICA 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 *) PROG (PARI) a(n)=sumdiv(n, k, if(k>1, moebius(k-1))) \\ Charles R Greathouse IV, Feb 07 2013 CROSSREFS Cf. A008683, A098035. Sequence in context: A111025 A271620 A374214 * A260073 A196306 A107093 Adjacent sequences: A098015 A098016 A098017 * A098019 A098020 A098021 KEYWORD sign AUTHOR Leroy Quet, Oct 24 2004 EXTENSIONS More terms from Robert G. Wilson v, Nov 01 2004 STATUS approved

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Last modified August 4 06:40 EDT 2024. Contains 374905 sequences. (Running on oeis4.)