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

1, 37044, 1222452, 193637687880

Offset: 1

Author

Farideh Firoozbakht, Dec 01 2005

Keywords

• more
• nonn

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

Examples

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

Crossrefs

Cf. A011257.

Programs

Mathematica

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

Extensions

a(4) from Giovanni Resta, Jul 13 2013