%I #7 Mar 03 2014 23:10:47
%S 48,512,540,1000,1836,2136,2176,2320,2340,3216,3648,3936,4284,4352,
%T 4356,4784,5088,5640,5936,6216,6576,6816,7120,7224,7280,7752,8100,
%U 8184,8496,8520,8760,9040,9296,9660,9680,9900,9996,10332,10860,11640,11680,11844
%N Numbers n such that phi(x) = n has exactly 11 solutions.
%H T. D. Noe, <a href="/A060674/b060674.txt">Table of n, a(n) for n = 1..1000</a>
%e 48 = phi(65) = phi(104) = phi(105) = phi(112) = phi(130) = phi(140) = phi(144) = phi(156) = phi(168) = phi(180) = phi(210).
%t a = Table[ 0, {12500} ]; Do[ p = EulerPhi[ n ]; If[ p < 12501, a[ [ p ] ]++ ], {n, 1, 50000} ]; Select[ Range[ 12500 ], a[ [ # ] ] == 11 & ]
%o (PARI) is(n)=sum(i=1,n,eulerphi(i)==n)==11 \\ _Charles R Greathouse IV_, Mar 03 2014
%Y Cf. A007366, A007367.
%K nonn
%O 1,1
%A _Robert G. Wilson v_, Apr 18 2001
