A015706 Odd numbers k that divide phi(k)*sigma(k).

1, 117, 135, 775, 819, 891, 1521, 1701, 2325, 3159, 3375, 4455, 5733, 6875, 6975, 10935, 11907, 19773, 20625, 20925, 22113, 22275, 24025, 40131, 41067, 43875, 44375, 49005, 61875, 62775, 68607, 72075, 75625, 83349, 84375, 85293

Offset: 1

Author

Robert G. Wilson v

Keywords

• nonn

Links

• Donovan Johnson, Table of n, a(n) for n = 1..3000
• Richard K. Guy, Divisors and desires, Amer. Math. Monthly, 104 (1997), 359-360.

Crossrefs

Cf. A011775.

Programs

Mathematica

Select[Range[1,85301,2],Divisible[EulerPhi[#]DivisorSigma[1,#],#]&] (* Harvey P. Dale, Aug 27 2013 *)

PARI

isok(n) = (n%2) && !(sigma(n)*eulerphi(n) % n); \\ Michel Marcus, Oct 02 2017