OFFSET
1,2
REFERENCES
J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 119, p. 41, Ellipses, Paris 2008.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..6000
EXAMPLE
phi(357) * sigma(357) = 110592 = 48^3.
MATHEMATICA
Select[Range[10^5], IntegerQ @ Surd[EulerPhi[#] * DivisorSigma[1, #], 3] &] (* Amiram Eldar, Sep 19 2019 *)
PROG
(PARI) isok(n) = ispower(eulerphi(n)*sigma(n), 3); \\ Michel Marcus, Jan 22 2014
(Magma) [k:k in [1..230000]| IsPower(EulerPhi(k)*DivisorSigma(1, k), 3)]; // Marius A. Burtea, Sep 19 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Giovanni Resta, Feb 13 2006
STATUS
approved