A065528 - OEIS

%I #21 Nov 08 2017 07:44:22

%S 5,8,10,12,15,16,17,20,24,30,32,34,37,40,48,51,57,60,63,64,68,74,76,

%T 80,85,96,101,102,108,114,120,125,126,128,136,160,170,185,192,197,202,

%U 204,219,240,247,250,255,256,257,259,272,273,285,292,296,304,315,320,327,333

%N Numbers n such that phi(n) is a nontrivial power b^c where b > 1 and c > 1.

%C What values of b can occur?

%C Apparently all even numbers can occur as values of b. Checked up to 50000; see A227533. - _Charles R Greathouse IV_, Jul 15 2013

%H Charles R Greathouse IV, <a href="/A065528/b065528.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A166955(n+2). - _Juri-Stepan Gerasimov_, Oct 25 2009

%e phi(63) = 6^2, phi(96) = 2^5.

%t ppQ[n_] := GCD @@ Last /@ FactorInteger@ n > 1; Select[ Range@ 330, ppQ@ EulerPhi@ # &] (* _Robert G. Wilson v_, Jul 16 2013 *)

%o (PARI) v=[]; for(n=2, 333, if(ispower(eulerphi(n)), v=concat(v, n))); v (Hobson)

%o (PARI) is(n)=ispower(eulerphi(n)) \\ _Charles R Greathouse IV_, Jul 15 2013

%Y Cf. A166955.

%K nonn,easy

%O 1,1

%A _Joseph L. Pe_, Nov 27 2001

%E More terms from Nick Hobson, Nov 29 2006

%E b-file from _Charles R Greathouse IV_, Mar 25 2010