OFFSET
1,2
COMMENTS
The number of terms below 10^3, 10^4, ... are 10, 44, 147, 397, ...
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
EXAMPLE
phi(150)=40, psi(150)=360, their arithmetic mean = 200, geometric mean = 120, harmonic mean = 72 are all integers.
MATHEMATICA
dedekindPsi[n_] := If[n < 1, 0, n Sum[MoebiusMu[d]^2/d, {d, Divisors@n}]];
aQ[n_] := Module[{s = dedekindPsi[n], p = EulerPhi[n]}, IntegerQ[(s + p)/2] && IntegerQ[Sqrt[s*p]] && IntegerQ[2 s*p/(s + p)]]; Select[Range[10^5], aQ]
CROSSREFS
KEYWORD
nonn
AUTHOR
Amiram Eldar, Sep 06 2017
STATUS
approved