OFFSET
1,7
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
From Amiram Eldar, Nov 19 2023: (Start)
a(n) = Sum_{d|n} Kronecker(18, d).
Multiplicative with a(p^e) = 1 if Kronecker(18, p) = 0 (p = 2 or 3), a(p^e) = (1+(-1)^e)/2 if Kronecker(18, p) = -1 (p is in A003629 \ {3}), and a(p^e) = e+1 if Kronecker(18, p) = 1 (p is in A001132).
Asymptotic mean: Limit_{m->oo} (1/m) * Sum_{k=1..m} a(k) = 4*log(sqrt(2)+1)/(3*sqrt(2)) = 0.830966986853... . (End)
MATHEMATICA
a[n_] := DivisorSum[n, KroneckerSymbol[18, #] &]; Array[a, 100] (* Amiram Eldar, Nov 19 2023 *)
PROG
(PARI) my(m = 18); direuler(p=2, 101, 1/(1-(kronecker(m, p)*(X-X^2))-X))
(PARI) a(n) = sumdiv(n, d, kronecker(18, d)); \\ Amiram Eldar, Nov 19 2023
CROSSREFS
KEYWORD
nonn,easy,mult
AUTHOR
STATUS
approved