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

1, 37044, 1222452, 193637687880

Offset

1,2

Comments

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

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

a(5) > 4*10^11. - Giovanni Resta, Jul 13 2013

Links

Table of n, a(n) for n=1..4.

Example

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

Mathematica

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

Crossrefs

Cf. A011257.

Sequence in context: A057881 A206051 A279862 * A250882 A219363 A254564

Adjacent sequences: A112725 A112726 A112727 * A112729 A112730 A112731

Keyword

more,nonn

Author

Farideh Firoozbakht, Dec 01 2005

Extensions

a(4) from Giovanni Resta, Jul 13 2013

Status

approved