A293605 Primes p such that phi(p-1) < (p-1)/4.

211, 331, 421, 631, 661, 991, 1051, 1171, 1321, 1471, 1951, 2311, 2341, 2521, 2731, 2971, 3121, 3301, 3361, 3511, 3571, 3631, 4201, 4621, 4831, 4951, 5281, 5851, 5881, 6007, 6091, 6271, 6301, 7351, 7411, 7561, 7591, 8191, 8581, 8779, 8821, 8971, 9241, 9283, 9661, 9871, 9901

Offset: 1

Author

Michel Marcus, Oct 13 2017

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000
• Tamiru Jarso and Tim Trudgian, Quadratic non-residues that are not primitive roots, Mathematics of Computation, Vol. 88, No. 317 (2019), pp. 1251-1260; arXiv preprint, arXiv:1710.04320 [math.NT], 2017.

Crossrefs

Cf. A000010, A008330, A241196.

Programs

Mathematica

Select[Prime[Range[1500]],EulerPhi[#-1]<(#-1)/4&] (* Harvey P. Dale, Oct 27 2018 *)

PARI

lista(nn) = forprime(p=2, nn, if (eulerphi(p-1) < (p-1)/4, print1(p, ", ")));