A067384 Numbers n such that sigma(phi(n))/sigma(n) = 4.

121679, 1043909, 2350171, 2918263, 3396103, 3566807, 3688067, 4019467, 4562827, 5963407, 7300697, 7485979, 7853933, 8103301, 8364151, 9237779, 9514213, 9638527, 10531123, 11094619, 11384447, 12721937, 13576267

Offset: 1

Author

Dean Hickerson, Jan 20 2002

Keywords

• nonn

Comments

Subsequence of A066881. - R. J. Mathar, Sep 30 2008

Links

• Donovan Johnson, Table of n, a(n) for n = 1..500

Crossrefs

Cf. A033631, A066831, A067382, A067383, A067385, A197952.

Programs

Mathematica

For[ n=1, True, n++, If[ DivisorSigma[ 1, EulerPhi[ n ] ]/DivisorSigma[ 1, n ]==4, Print[ n ] ] ]

PARI

is(n)=sigma(phi(n=factor(n)))/sigma(n)==4 \\ Charles R Greathouse IV, Nov 27 2013