A067383 Numbers n such that sigma(phi(n))/sigma(n) = 3.

181, 899, 2501, 4687, 10991, 12989, 17653, 25199, 25853, 26549, 26657, 54473, 65941, 68381, 72007, 82777, 96197, 98903, 102719, 116449, 124013, 135907, 150121, 169153, 188917, 193553, 201173, 207461, 219559, 234301, 237961, 239279

Offset: 1

Author

Dean Hickerson, Jan 20 2002

Keywords

• nonn

Links

• Donovan Johnson, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A033631, A066831, A067382, A067384, A067385, A197952.

Programs

Mathematica

For[ n=1, True, n++, If[ DivisorSigma[ 1, EulerPhi[ n ] ]/DivisorSigma[ 1, n ]==3, Print[ n ] ] ]
Select[Range[250000],DivisorSigma[1,EulerPhi[#]]/DivisorSigma[1,#]==3&] (* Harvey P. Dale, Sep 08 2024 *)

PARI

is(n)=sigma(eulerphi(n=factor(n)))/sigma(n)==3 \\ Charles R Greathouse IV, Nov 27 2013