A066994 Numbers k such that phi(k) divides k*sigma(k).

1, 2, 3, 4, 6, 8, 10, 12, 14, 15, 16, 18, 20, 21, 24, 26, 27, 30, 32, 35, 36, 39, 40, 42, 48, 54, 55, 56, 60, 63, 64, 70, 72, 78, 80, 84, 88, 96, 98, 104, 105, 108, 110, 114, 116, 120, 125, 126, 128, 135, 140, 144, 147, 150, 155, 156, 160, 162, 165, 168, 189, 190, 192

Offset: 1

Author

Benoit Cloitre, Jan 27 2002

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Harry J. Smith)

Crossrefs

Cf. A000010 (phi), A000203 (sigma), A011775.

Subsequences: A007694, A020492.

Programs

Mathematica

Select[Range[200],Divisible[# DivisorSigma[1,#],EulerPhi[#]]&] (* Harvey P. Dale, Aug 23 2019 *)

PARI

isok(k) = { (k*sigma(k)) % eulerphi(k) == 0 } \\ Harry J. Smith, Apr 23 2010

Extensions

Missing term a(7)=10 added by Harry J. Smith, Apr 23 2010