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%I #8 Oct 05 2015 09:30:42
%S 160,168,352,448,816,928,972,1024,1176,1848,2464,3040,3808,4152,4440,
%T 4512,4736,4944,5104,5152,5160,5304,5952,6408,6656,6672,6784,7648,
%U 8384,8704,8904,10432,10528,10624,11000,11008,11456,11776,12048,12416,13024,13032
%N Numbers n such that phi(x) = n has exactly 12 solutions.
%H T. D. Noe, <a href="/A060675/b060675.txt">Table of n, a(n) for n = 1..1000</a>
%e 160 = phi(187) = phi(205) = phi(328) = phi(352) = phi(374) = phi(400) = phi(410) = phi(440) = phi(492) = phi(528) = phi(600) = phi(660).
%t a = Table[ 0, {15000} ]; Do[ p = EulerPhi[ n ]; If[ p < 15001, a[ [ p ] ]++ ], {n, 1, 60000} ]; Select[ Range[ 15000 ], a[ [ # ] ] == 12 & ]
%t Union[Transpose[Select[Tally[EulerPhi[Range[100000]]],#[[2]]==12&]][[1]]] (* _Harvey P. Dale_, Oct 05 2015 *)
%o (PARI) is(n)=sum(i=1,n,eulerphi(i)==n)==12 \\ _Charles R Greathouse IV_, Mar 03 2014
%Y Cf. A007366, A007367.
%K nonn
%O 1,1
%A _Robert G. Wilson v_, Apr 18 2001
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