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Numbers k such that there are no numbers with k primitive roots.
2

%I #13 Oct 03 2021 04:58:40

%S 3,5,7,9,11,13,14,15,17,19,21,23,25,26,27,29,30,31,33,34,35,37,38,39,

%T 41,42,43,45,46,47,49,50,51,53,55,56,57,58,59,61,62,63,65,66,67,68,69,

%U 70,71,73,74,75,76,77,78,79,81,83,85,86,87,89,90,91,93,94,95

%N Numbers k such that there are no numbers with k primitive roots.

%C Numbers k such that A231772(k) = 0.

%H Amiram Eldar, <a href="/A231773/b231773.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A007617(n) for n <= 16.

%o (PARI) r=95; for(n=2, r, m=0; for(c=2*n+1, n^2+1, if(n%2==1, break); e=eulerphi(c); if(e==lcm(znstar(c)[2])&&eulerphi(e)==n, m=1; break)); if(m==0, print1(n, ", ")));

%Y Cf. A007617, A010554, A046144, A231772.

%K nonn

%O 1,1

%A _Arkadiusz Wesolowski_, Nov 13 2013