A063469 - OEIS

A063469

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

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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

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

LINKS

Table of n, a(n) for n=1..10.

MATHEMATICA

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

PROG

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

CROSSREFS

Cf. A062516.

Cf. A112954, A020488, A063470.

Sequence in context: A097182 A058525 A219036 * A155131 A160890 A319527

Adjacent sequences: A063466 A063467 A063468 * A063470 A063471 A063472

KEYWORD

fini,full,nonn

AUTHOR

Jason Earls, Jul 26 2001

EXTENSIONS

"full" keyword from Max Alekseyev, Mar 01 2010

STATUS

approved