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%I #13 Oct 12 2021 08:01:05
%S 211,331,421,631,661,991,1051,1171,1321,1471,1951,2311,2341,2521,2731,
%T 2971,3121,3301,3361,3511,3571,3631,4201,4621,4831,4951,5281,5851,
%U 5881,6007,6091,6271,6301,7351,7411,7561,7591,8191,8581,8779,8821,8971,9241,9283,9661,9871,9901
%N Primes p such that phi(p-1) < (p-1)/4.
%H Amiram Eldar, <a href="/A293605/b293605.txt">Table of n, a(n) for n = 1..10000</a>
%H Tamiru Jarso and Tim Trudgian, <a href="https://doi.org/10.1090/mcom/3378">Quadratic non-residues that are not primitive roots</a>, Mathematics of Computation, Vol. 88, No. 317 (2019), pp. 1251-1260; <a href="https://arxiv.org/abs/1710.04320">arXiv preprint</a>, arXiv:1710.04320 [math.NT], 2017.
%t Select[Prime[Range[1500]],EulerPhi[#-1]<(#-1)/4&] (* _Harvey P. Dale_, Oct 27 2018 *)
%o (PARI) lista(nn) = forprime(p=2, nn, if (eulerphi(p-1) < (p-1)/4, print1(p, ", ")));
%Y Cf. A000010, A008330, A241196.
%K nonn
%O 1,1
%A _Michel Marcus_, Oct 13 2017
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