OFFSET
1,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..719
FORMULA
a(n) = Sum_{x_1|n, x_2|n, ... , x_n|n} n/lcm(x_1,x_2, ... ,x_n).
a(n) = Sum_{d|n} phi(n/d) * tau(d)^n.
If p is prime, a(p) = 2^p - 1 + p.
a(n) = Sum_{k=1..n} tau(gcd(k,n))^n.
MATHEMATICA
a[n_] := DivisorSum[n, EulerPhi[n/#] * DivisorSigma[0, #]^n &]; Array[a, 20] (* Amiram Eldar, May 10 2021 *)
PROG
(PARI) a(n) = sumdiv(n, d, eulerphi(n/d)*numdiv(d)^n);
(PARI) a(n) = sum(k=1, n, numdiv(gcd(k, n))^n);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, May 10 2021
STATUS
approved