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A112728 Numbers n such that geometric mean of phi(n), n and sigma(n) is an integer. 0
1, 37044, 1222452, 193637687880 (list; graph; refs; listen; history; text; internal format)
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

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Last modified August 6 08:22 EDT 2020. Contains 336228 sequences. (Running on oeis4.)