A067878 Numbers k such that sigma(k) = phi(k*omega(k)-1).

1, 10, 33, 46, 65, 77, 123, 136, 221, 371, 385, 423, 513, 532, 545, 572, 660, 702, 753, 1248, 1566, 1643, 1720, 2033, 2635, 3243, 4533, 4798, 5177, 5346, 5495, 5605, 6460, 7463, 7565, 7683, 7739, 8201, 9342, 9741, 10780, 10792, 11679, 11880, 12256

Offset: 1

Author

Benoit Cloitre, Mar 02 2002

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000010 (phi), A000203 (sigma), A001221 (omega), A328260.

Programs

Mathematica

Select[Range[13000],DivisorSigma[1,#]==EulerPhi[#*PrimeNu[#]-1]&] (* Harvey P. Dale, Feb 02 2015 *)

PARI

isok(k) = {my(f = factor(k)); sigma(f) == eulerphi(k * omega(f) - 1);} \\ Amiram Eldar, Apr 25 2025