A069058 Numbers n such that A017666(n)=phi(n).

1, 18, 72, 162, 648, 1152, 1458, 4608, 5832, 10368, 13122, 41472, 52488, 73728, 93312, 118098, 294912, 373248, 472392, 663552, 839808, 1062882, 2654208, 3359232, 4251528, 4718592, 5971968, 7558272, 9565938, 18874368, 23887872

Offset: 1

Author

Benoit Cloitre, Apr 04 2002

Keywords

• easy
• nonn

Comments

Appears to be a subset of A195321, i.e. all terms greater than 1 are of the form 18*n^2. - William J. Keith, May 25 2016

It also appears to be a subset of A003586, i.e., all the terms below 10^12 are of the form 2^i*3^j. - Giovanni Resta, May 26 2016

Links

• Giovanni Resta, Table of n, a(n) for n = 1..81 (terms < 10^12)

Crossrefs

Cf. A195321.

Programs

Mathematica

Select[Range[10^6], Denominator@ Total[1/Divisors@ #] == EulerPhi@ # &] (* Michael De Vlieger, May 25 2016 *)

PARI

for(n=1, 2500000, if(denominator(sumdiv(n,k,1/k)) == eulerphi(n), print1(n,",")))

PARI

isok(n) = denominator(sigma(n)/n) == eulerphi(n); \\ Michel Marcus, May 26 2016

Extensions

More terms from Rick L. Shepherd, Apr 16 2002