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A116007
Numbers k such that k + sigma(k) + phi(k) is a fourth power.
3
81, 18904, 176705, 204576, 534160, 1362561, 1366633, 1698256, 1866768, 2034576, 2523024, 2909656, 3380856, 7217649, 9439473, 9454609, 11197696, 12866040, 29508673, 32363424, 34142545, 34682089, 46426160, 46448824, 53445456, 57807984, 58298881, 81378529, 98156353
OFFSET
1,1
LINKS
EXAMPLE
81 + sigma(81) + phi(81) = 4^4.
MATHEMATICA
Select[Range[2*10^6], IntegerQ[Surd[# + DivisorSigma[1, #] + EulerPhi[#], 4]] &] (* Amiram Eldar, Dec 15 2023 *)
PROG
(PARI) isok(n) = ispower(n + sigma(n) + eulerphi(n), 4); \\ Michel Marcus, Jan 25 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Giovanni Resta, Feb 13 2006
EXTENSIONS
a(15)-a(25) from Donovan Johnson, Jul 02 2010
a(26)-a(29) from Amiram Eldar, Dec 15 2023
STATUS
approved