A035208 - OEIS

%I #9 Nov 19 2023 01:24:48

%S 1,1,0,1,2,0,0,1,1,2,2,0,1,0,0,1,2,1,2,2,0,2,2,0,3,1,0,0,0,0,0,1,0,2,

%T 0,1,2,2,0,2,0,0,0,2,2,2,0,0,1,3,0,1,0,0,4,0,0,0,2,0,0,0,0,1,2,0,2,2,

%U 0,0,0,1,0,2,0,2,0,0,2,2,1

%N Coefficients in expansion of Dirichlet series Product_p (1-(Kronecker(m,p)+1)*p^(-s)+Kronecker(m,p)*p^(-2s))^(-1) for m = 26.

%H Amiram Eldar, <a href="/A035208/b035208.txt">Table of n, a(n) for n = 1..10000</a>

%F From _Amiram Eldar_, Nov 19 2023: (Start)

%F a(n) = Sum_{d|n} Kronecker(26, d).

%F Multiplicative with a(p^e) = 1 if Kronecker(26, p) = 0 (p = 2 or 13), a(p^e) = (1+(-1)^e)/2 if Kronecker(26, p) = -1 (p is in A038900), and a(p^e) = e+1 if Kronecker(26, p) = 1 (p is in A038899 \ {2, 13}).

%F Asymptotic mean: Limit_{m->oo} (1/m) * Sum_{k=1..m} a(k) = 2*log(sqrt(26)+5)/sqrt(26) = 0.907012940471... . (End)

%t a[n_] := DivisorSum[n, KroneckerSymbol[26, #] &]; Array[a, 100] (* _Amiram Eldar_, Nov 19 2023 *)

%o (PARI) my(m = 26); direuler(p=2,101,1/(1-(kronecker(m,p)*(X-X^2))-X))

%o (PARI) a(n) = sumdiv(n, d, kronecker(26, d)); \\ _Amiram Eldar_, Nov 19 2023

%Y Cf. A038899, A038900.

%K nonn,easy,mult

%O 1,5

%A _N. J. A. Sloane_