A165630 Numbers n such that sigma(n)/phi(n) = 25/9, where sigma = A000203, phi = A000010.

8721, 10179, 21489, 99813, 203721, 228417, 229653, 250705, 268047, 609957, 1150713, 1343277, 2429283, 2835417, 2835807, 2881197, 3150333, 3230469, 3833181, 4679157, 4885569, 5673291, 6082527, 6302529, 6713637, 6819879, 7096329, 9464121, 10313979, 12168651

Offset: 1

Author

Farideh Firoozbakht and M. F. Hasler, Sep 23 2009

Keywords

• nonn

Comments

A subsequence of A011257. Contains the product m*n of relatively prime (gcd(m,n)=1) terms (m,n) in A164647 x A164648.

Links

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

Programs

Mathematica

Select[Range[122*10^5],DivisorSigma[1,#]/EulerPhi[#]==25/9&] (* Harvey P. Dale, Jun 20 2021 *)

PARI

for( i=1,1e7, sigma(i)/eulerphi(i)==25/9 && print1(i", "))