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A114078
Numbers k such that phi(k)*sigma(k) is a fourth power.
2
1, 170, 595, 714, 121056, 480441, 529620, 706063, 706237, 729752, 755972, 815654, 2162808, 2449062, 2827789, 2927848, 2957416, 2994681, 2995419, 3010227, 3019028, 3019772, 3080140, 3093860, 3103464, 3206364, 3213804
OFFSET
1,2
REFERENCES
J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 170, p. 54, Ellipses, Paris 2008.
LINKS
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
Cf. A062354, subsequence of A011257.
Sequence in context: A364905 A362561 A045089 * A031704 A173275 A301867
KEYWORD
nonn
AUTHOR
Giovanni Resta, Feb 13 2006
STATUS
approved