%I #7 Mar 03 2014 23:09:09
%S 32,132,156,544,912,924,1012,1044,1140,1452,1464,1472,1476,1572,1664,
%T 1764,2076,2100,2232,2424,2580,2624,2652,3096,3248,3336,3444,3660,
%U 3996,4488,4776,4840,5060,5316,5412,5696,6504,6516,6540,6612,6660,6780,6996,7116
%N Numbers n such that phi(x) = n has exactly 7 solutions.
%H T. D. Noe, <a href="/A060670/b060670.txt">Table of n, a(n) for n = 1..1000</a>
%e 32 = phi(51) = phi(64) = phi(68) = phi(80) = phi(96) = phi(102) = phi(120).
%t a = Table[ 0, {8000} ]; Do[ p = EulerPhi[ n ]; If[ p < 8001, a[ [ p ] ]++ ], {n, 1, 25000} ]; Select[ Range[ 8000 ], a[ [ # ] ] == 7 & ]
%o (PARI) is(n)=sum(i=1,n,eulerphi(i)==n)==7 \\ _Charles R Greathouse IV_, Mar 03 2014
%Y Cf. A007366, A007367.
%K nonn
%O 1,1
%A _Robert G. Wilson v_, Apr 18 2001