A073858 Numbers k such that sigma(phi(k)) divides phi(sigma(k)).

1, 2, 4, 9, 16, 18, 64, 100, 225, 242, 450, 516, 729, 1458, 3872, 4096, 4624, 13932, 14406, 17672, 18225, 20124, 21780, 28900, 29262, 29616, 36450, 45996, 62500, 65025, 65536, 76832, 92778, 95916, 106092, 106308, 114630, 114930

Offset: 1

Author

Benoit Cloitre, Sep 02 2002

Keywords

• easy
• nonn

Links

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

Crossrefs

Cf. A033632, A066930.

Programs

Mathematica

Select[Range[115000],Divisible[EulerPhi[DivisorSigma[1,#]],DivisorSigma[ 1,EulerPhi[ #]]]&] (* Harvey P. Dale, Jan 31 2021 *)

PARI

isok(k) = eulerphi(sigma(k)) % sigma(eulerphi(k))==0 \\ Donovan Johnson, Jul 05 2012