%I #12 Nov 18 2023 06:30:42

%S 1,2,1,3,1,2,2,4,1,2,2,3,0,4,1,5,2,2,0,3,2,4,0,4,1,0,1,6,0,2,0,6,2,4,

%T 2,3,0,0,0,4,0,4,2,6,1,0,0,5,3,2,2,0,2,2,2,8,0,0,2,3,2,0,2,7,0,4,2,6,

%U 0,4,2,4,0,0,1,0,4,0,0,5,1

%N Coefficients in expansion of Dirichlet series Product_p (1-(Kronecker(m,p)+1)*p^(-s)+Kronecker(m,p)*p^(-2s))^(-1) for m = 15.

%H G. C. Greubel, <a href="/A035197/b035197.txt">Table of n, a(n) for n = 1..10000</a>

%F From _Amiram Eldar_, Nov 18 2023: (Start)

%F a(n) = Sum_{d|n} Kronecker(15, d).

%F Multiplicative with a(p^e) = 1 if Kronecker(15, p) = 0 (p = 3 or 5), a(p^e) = (1+(-1)^e)/2 if Kronecker(15, p) = -1 (p is in A038888), and a(p^e) = e+1 if Kronecker(15, p) = 1 (p is in A038887 \ {3, 5}).

%F Asymptotic mean: Limit_{m->oo} (1/m) * Sum_{k=1..m} a(k) = 4*log(sqrt(15)+4)/sqrt(15) = 2.131108641007... . (End)

%t a[n_] := If[n < 0, 0, DivisorSum[n, KroneckerSymbol[15, #] &]]; Table[ a[n], {n, 1, 100}] (* _G. C. Greubel_, Apr 27 2018 *)

%o (PARI) my(m=15); direuler(p=2,101,1/(1-(kronecker(m,p)*(X-X^2))-X))

%o (PARI) a(n) = sumdiv(n, d, kronecker(15, d)); \\ _Amiram Eldar_, Nov 18 2023

%Y Cf. A038887, A038888.

%K nonn,easy,mult

%O 1,2

%A _N. J. A. Sloane_