

A112728


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


0




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



