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 A327276 a(n) = Sum_{d|n, d odd} mu(d) * mu(n/d). 4
 1, -1, -2, 0, -2, 2, -2, 0, 1, 2, -2, 0, -2, 2, 4, 0, -2, -1, -2, 0, 4, 2, -2, 0, 1, 2, 0, 0, -2, -4, -2, 0, 4, 2, 4, 0, -2, 2, 4, 0, -2, -4, -2, 0, -2, 2, -2, 0, 1, -1, 4, 0, -2, 0, 4, 0, 4, 2, -2, 0, -2, 2, -2, 0, 4, -4, -2, 0, 4, -4, -2, 0, -2, 2, -2, 0, 4, -4, -2 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Dirichlet inverse of A001227. All terms are 0 or +/- a power of 2. - Robert Israel, Nov 26 2019 LINKS Robert Israel, Table of n, a(n) for n = 1..10000 FORMULA G.f. A(x) satisfies: A(x) = x - Sum_{k>=2} A001227(k) * A(x^k). Dirichlet g.f.: 1 / (zeta(s)^2 * (1 - 1/2^s)). a(1) = 1; a(n) = -Sum_{d|n, d 1, and a(p^e) = -2 if e = 1, 1 if e = 2, and 0 if e > 2, for an odd prime p. - Amiram Eldar, Oct 25 2020 MAPLE f:= proc(n) local m, d;   m:= n/2^padic:-ordp(n, 2);   add(numtheory:-mobius(d)*numtheory:-mobius(n/d), d = numtheory:-divisors(m)) end proc: map(f, [\$1..100]); # Robert Israel, Nov 26 2019 MATHEMATICA Table[DivisorSum[n, MoebiusMu[#] MoebiusMu[n/#] &, OddQ[#] &], {n, 1, 79}] a[n_] := If[n == 1, n, -Sum[If[d < n, DivisorSum[n/d, Mod[#, 2] &] a[d], 0], {d, Divisors[n]}]]; Table[a[n], {n, 1, 79}] f[p_, e_] := Which[e == 1, -1 - Boole[p > 2], e == 2, Boole[p > 2], e > 2, 0]; a[1] = 1; a[n_] := Times @@ (f @@@ FactorInteger[n]); Array[a, 100] (* Amiram Eldar, Oct 25 2020 *) PROG (MAGMA) [&+[MoebiusMu(d)*MoebiusMu(n div d): d in [a:a in Divisors(n)| IsOdd(a)]]:n in [1..80]]; // Marius A. Burtea, Sep 15 2019 (PARI) a(n)={sumdiv(n, d, if(d%2, moebius(d)*moebius(n/d)))} \\ Andrew Howroyd, Sep 23 2019 CROSSREFS Cf. A001227, A007427, A008683, A068068, A209229, A327278. Sequence in context: A341846 A262670 A082054 * A044943 A292118 A277486 Adjacent sequences:  A327273 A327274 A327275 * A327277 A327278 A327279 KEYWORD sign,mult,easy AUTHOR Ilya Gutkovskiy, Sep 15 2019 STATUS approved

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Last modified June 24 18:46 EDT 2021. Contains 345419 sequences. (Running on oeis4.)