OFFSET
1,2
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..10000
FORMULA
From Amiram Eldar, Oct 17 2022: (Start)
a(n) = Sum_{d|n} Kronecker(7, d).
Asymptotic mean: Limit_{m->oo} (1/m) * Sum_{k=1..m} a(k) = 2*log(8+3*sqrt(7)) / sqrt(7) = 2.0929097... . (End)
Multiplicative with a(7^e) = 1, a(p^e) = (1+(-1)^e)/2 if Kronecker(7, p) = -1 (p is in A003632), and a(p^e) = e+1 if Kronecker(7, p) = 1 (p is in A038878 \ {7}). - Amiram Eldar, Nov 20 2023
MATHEMATICA
a[n_] := If[n < 0, 0, DivisorSum[n, KroneckerSymbol[7, #] &]]; Table[ a[n], {n, 1, 100}] (* G. C. Greubel, Apr 27 2018 *)
PROG
(PARI) my(m=7); direuler(p=2, 101, 1/(1-(kronecker(m, p)*(X-X^2))-X))
(PARI) a(n) = sumdiv(n, d, kronecker(7, d)); \\ Amiram Eldar, Nov 20 2023
CROSSREFS
KEYWORD
nonn,easy,mult
AUTHOR
STATUS
approved