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%I #12 Jul 15 2024 22:54:09
%S 1,2,8,10,20,22,28,30,32,44,46,48,52,54,56,58,66,70,72,78,82,92,96,
%T 102,104,106,110,116,120,126,130,132,136,138,140,148,150,156,164,166,
%U 172,178,190,196,198,204,210,212,216,220,222,226,228,238,240,250,260,262
%N Numbers k such that the cardinality of the set of solutions to phi(x) = k is a prime.
%C All terms except 1 are even. - _Robert Israel_, Mar 29 2020
%H Robert Israel, <a href="/A071388/b071388.txt">Table of n, a(n) for n = 1..10000</a>
%e InvPhi[48]={65,104,105,112,130,140,144,156,168,180,210} has 11 terms, so 48 is here.
%p filter:= n -> isprime(nops(numtheory:-invphi(n))):
%p select(filter, [$1..400]); # _Robert Israel_, Mar 29 2020
%Y Cf. A000010, A007366, A007367, A014197, A058277, A060668, A060670, A060674, A063512, A071386-A071389.
%K nonn
%O 1,2
%A _Labos Elemer_, May 23 2002
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