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A112728 Numbers n such that geometric mean of phi(n), n and sigma(n) is an integer. 0

%I

%S 1,37044,1222452,193637687880

%N Numbers n such that geometric mean of phi(n), n and sigma(n) is an integer.

%C It is interesting that a(2) divides a(3).

%C There is no further term up to 6*10^8.

%C a(5) > 4*10^11. - _Giovanni Resta_, Jul 13 2013

%e (phi(1222452)*1222452*sigma(1222452))^(1/3)=1164240 is an integer, so 1222452 is a term of the sequence.

%t Do[If[IntegerQ[(n*DivisorSigma[1, n] EulerPhi[n])^(1/3)], Print[n]], {n, 600000000}]

%Y Cf. A011257.

%K more,nonn

%O 1,2

%A _Farideh Firoozbakht_, Dec 01 2005

%E a(4) from _Giovanni Resta_, Jul 13 2013

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Last modified February 4 12:59 EST 2023. Contains 360055 sequences. (Running on oeis4.)