A073858 - OEIS

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

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OFFSET

1,2

LINKS

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

MATHEMATICA

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

PROG

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

CROSSREFS

Cf. A033632, A066930.

Sequence in context: A337343 A379112 A015730 * A006474 A110878 A253849

Adjacent sequences: A073855 A073856 A073857 * A073859 A073860 A073861

KEYWORD

easy,nonn

AUTHOR

Benoit Cloitre, Sep 02 2002

STATUS

approved