OFFSET
1,2
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = Sum_{1 <= x_1, x_2 <= n} sigma( ( gcd(x_1, n)/gcd(x_1, x_2, n) )^2 ).
a(n) = Sum_{d|n} J_2(d) * sigma(d), where the Jordan totient function J_2(n) = A007434(n).
From Amiram Eldar, May 26 2024: (Start)
Multiplicative with a(p^e) = (p^(3*e+2)*(p+1) - p^(2*e)*(p^2+p+1) + p)/(p^3-1).
Sum_{k=1..n} a(k) ~ c * n^4 / 4, where c = zeta(4) * Product_{p prime} (1 + 1/p^2 - 1/p^3) = 1.41347980562116709395... . (End)
MATHEMATICA
f[p_, e_] := (p^(3*e + 2)*(p+1) - p^(2*e)*(p^2+p+1) + p)/(p^3-1); a[1] = 1; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 100] (* Amiram Eldar, May 26 2024 *)
PROG
(PARI) J(n, k) = sumdiv(n, d, d^k*moebius(n/d));
a(n, k=2, m=1) = sumdiv(n, d, J(d, k)*sigma(d^m));
CROSSREFS
KEYWORD
nonn,mult
AUTHOR
Seiichi Manyama, May 26 2024
STATUS
approved