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

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

KEYWORD

more,nonn

AUTHOR

Farideh Firoozbakht, Dec 01 2005

EXTENSIONS

a(4) from Giovanni Resta, Jul 13 2013

STATUS

approved