A066995 Numbers k such that sigma(k) divides k*phi(k).

1, 6, 15, 28, 84, 95, 140, 182, 190, 248, 270, 287, 308, 357, 420, 455, 477, 496, 570, 672, 744, 819, 840, 910, 1199, 1428, 1488, 1547, 1638, 1722, 1848, 1892, 2295, 2398, 2480, 2660, 2730, 3339, 3417, 3472, 3515, 3596, 3640, 3720, 3780, 3956, 4064, 4095

Offset: 1

Author

Benoit Cloitre, Jan 27 2002

Keywords

• nonn

Links

• Harry J. Smith, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A001599, A011775.

Programs

GAP

Filtered([1..10^5], n ->  n*Phi(n) mod Sigma(n) = 0); # Muniru A Asiru, Jan 31 2018

Mathematica

Select[Range[4500],Divisible[# EulerPhi[#],DivisorSigma[1,#]]&]  (* Harvey P. Dale, Mar 19 2011 *)

PARI

isok(n) = frac(n*eulerphi(n)/sigma(n)) == 0; \\ Michel Marcus, Jan 31 2018