A063469 Numbers n such that tau(n)*3 = phi(n).

7, 21, 26, 56, 70, 78, 108, 126, 168, 210

Offset: 1

Author

Jason Earls, Jul 26 2001

Keywords

• fini
• full
• nonn

Comments

"phi(n)=k*Tau[n] has at most finitely many solutions for any constant k or even for slowly increasing functions like k(n)=n^(epsilon)." - Labos Elemer, Jul 20 2001

Crossrefs

Cf. A062516.

Cf. A112954, A020488, A063470.

Programs

Mathematica

Select[Range[300],3DivisorSigma[0,#]==EulerPhi[#]&] (* Harvey P. Dale, Sep 15 2016 *)

PARI

for(n=1,10^7, if(3*numdiv(n)==eulerphi(n),print(n)))

Extensions

"full" keyword from Max Alekseyev, Mar 01 2010