OFFSET
1,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..388
FORMULA
a(n) = Sum_{d|n} phi(n/d) * phi(d)^(d-1).
If p is prime, a(p) = p-1 + (p-1)^(p-1).
MATHEMATICA
a[n_] := DivisorSum[n, EulerPhi[n/#] * EulerPhi[#]^(# - 1) &]; Array[a, 20] (* Amiram Eldar, Mar 15 2021 *)
PROG
(PARI) a(n) = sum(k=1, n, eulerphi(gcd(k, n))^(gcd(k, n)-1));
(PARI) a(n) = sumdiv(n, d, eulerphi(n/d)*eulerphi(d)^(d-1));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Mar 15 2021
STATUS
approved