A165629 Numbers n such that sigma(n)/phi(n) = 25/4, where sigma = A000203, phi = A000010.

760, 11020, 18088, 21112, 58206, 65262, 71630, 100280, 123424, 142688, 262276, 303212, 332710, 630344, 679070, 761390, 1265096, 1369120, 1454060, 1454260, 1462552, 1704794, 2185750, 2386664, 2627548, 2783872, 2786056, 2909380, 2927848, 5207680, 5289220

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 A068390 x A164648 and in A164646 x A165630.

Links

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

Programs

Mathematica

Select[Range[5300000],4*DivisorSigma[1,#]==25*EulerPhi[#]&] (* Harvey P. Dale, May 09 2012 *)

PARI

for( i=1,1e9, sigma(i)*4-25*eulerphi(i) || print1(i", "))