OFFSET
1,2
REFERENCES
J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 170, p. 54, Ellipses, Paris 2008.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..600
EXAMPLE
phi(595) * sigma(595) = 331776 = 24^4.
MATHEMATICA
Select[Range[3300000], IntegerQ[Power[EulerPhi[#] DivisorSigma[1, #], (4)^-1]]&] (* Harvey P. Dale, Mar 14 2011 *)
PROG
(PARI) isok(n) = ispower(eulerphi(n)*sigma(n), 4); \\ Michel Marcus, Jan 09 2014
(Magma) [k:k in [1..3300000]| IsPower(EulerPhi(k)*DivisorSigma(1, k), 4)]; // Marius A. Burtea, Sep 19 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Giovanni Resta, Feb 13 2006
STATUS
approved