OFFSET
1,3
COMMENTS
Denoted by |lambda(n)| on page 4 (1.7) in Kassel and Reutenauer arXiv:1610.07793. - Michael Somos, Jun 04 2015
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..16384
Christian Kassel and Christophe Reutenauer, The zeta function of the Hilbert scheme of n points on a two-dimensional torus, arXiv:1505.07229v3 [math.AG], 2015. [Note that a later version of this paper has a different title and different contents, and the number-theoretical part of the paper was moved to the publication which is next in this list.]
Christian Kassel and Christophe Reutenauer, Complete determination of the zeta function of the Hilbert scheme of n points on a two-dimensional torus, arXiv:1610.07793 [math.NT], 2016.
FORMULA
Moebius transform is period 9 sequence [ 1, -1, 1, 1, -1, -1, 1, -1, 0, ...].
a(n) is multiplicative with a(p^e) = 2 if p = 3 and e>0, a(p^e) = e+1 if p == 1 (mod 6), a(p^e) = (1 + (-1)^e) / 2 if p == 2, 5 (mod 6).
3 * a(n) = A113062(n) unless n=0.
G.f.: Sum_{k>0} f(x^k) + f(x^(3*k)) where f(x) := x / (1 + x + x^2). - Michael Somos, Jun 04 2015
a(n) = |A123477(n)|. - Michael Somos, Dec 10 2017
Asymptotic mean: Limit_{m->oo} (1/m) * Sum_{k=1..m} a(k) = 4*Pi/(9*sqrt(3)) = 0.806133... (A121839 - 1). - Amiram Eldar, Dec 28 2023
EXAMPLE
G.f. = x + 2*x^3 + x^4 + 2*x^7 + 2*x^9 + 2*x^12 + 2*x^13 + x^16 + 2*x^19 + ...
MATHEMATICA
a[ n_] := If[ n < 1, 0, DivisorSum[ n, {1, -1, 1, 1, -1, -1, 1, -1, 0} [[Mod[#, 9, 1]]] &]]; (* Michael Somos, Jun 04 2015 *)
f[p_, e_] := If[Mod[p, 6] == 1, e+1, (1+(-1)^e)/2]; f[3, e_] := 2; a[n_] := Times @@ f @@@ FactorInteger[n]; a[1] = 1; Array[a, 100] (* Amiram Eldar, Sep 05 2023 *)
PROG
(PARI) {a(n) = if( n<1, 0, sumdiv(n, d, [0, 1, -1, 1, 1, -1, -1, 1, -1][d%9 + 1]))};
(PARI) {a(n) = my(A, p, e); if( n<1, 0, A = factor(n); prod(k=1, matsize(A)[1], [p, e] = A[k, ]; if( p==3, 2, p%6==1, e+1, !(e%2))))};
CROSSREFS
KEYWORD
nonn,easy,mult
AUTHOR
Michael Somos, Oct 13 2005
STATUS
approved