OFFSET
1,2
COMMENTS
Moebius transform of A162395.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
G.f.: Sum_{k>=1} mu(k) * x^k * (1 - x^k) / (1 + x^k)^3.
G.f. A(x) satisfies: A(x) = x * (1 - x) / (1 + x)^3 - Sum_{k>=2} A(x^k).
Dirichlet g.f.: (1 - 2^(3 - s)) * zeta(s - 2) / zeta(s).
a(n) = J_2(n) if n odd, J_2(n) - 8 * J_2(n/2) if n even, where J_2 = A007434 (Jordan function J_2).
Multiplicative with a(2) = -5, a(2^e) = -3*2^(2*(e-1)) for e > 1, and a(p^e) = (p^2-1)*p^(2*(e-1)) for p > 2. - Amiram Eldar, Nov 15 2022
MATHEMATICA
Table[n^2 Sum[(-1)^(n/d + 1) MoebiusMu[d]/d^2, {d, Divisors[n]}], {n, 1, 50}]
nmax = 50; CoefficientList[Series[Sum[MoebiusMu[k] x^k (1 - x^k)/(1 + x^k)^3, {k, 1, nmax}], {x, 0, nmax}], x] // Rest
f[p_, e_] := (p^2 - 1)*p^(2*(e - 1)); f[2, 1] = -5; f[2, e_] := -3*2^(2*(e - 1)); a[1] = 1; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 100] (* Amiram Eldar, Nov 15 2022 *)
PROG
(PARI) a(n) = n^2 * sumdiv(n, d, (-1)^(n/d+1)*moebius(d)/d^2); \\ Michel Marcus, Nov 02 2020
CROSSREFS
KEYWORD
sign,mult
AUTHOR
Ilya Gutkovskiy, Nov 02 2020
STATUS
approved