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%I #31 Aug 30 2019 21:50:41
%S 29,197,211,379,421,491,547,659,701,757,827,883,1373,1499,1667,1877,
%T 2213,2269,2339,2437,2549,2843,3011,3067,3347,3557,3571,3613,3851,
%U 3907,4019,4229,4243,4397,4621,4691,4789,4957,5573,5741,5923,6203,6469,6637,6763,6917
%N Primes p such that 2 is a primitive root modulo p while 128 is not.
%C Primes p such that 2 is a primitive root modulo p (i.e., p is in A001122) and that p == 1 (mod 7).
%C According to Artin's conjecture, the number of terms <= N is roughly ((6/41)*C)*PrimePi(N), where C is the Artin's constant = A005596, PrimePi = A000720. Compare: the number of terms of A001122 that are no greater than N is roughly C*PrimePi(N).
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/ArtinsConstant.html">Artin's constant</a>
%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Artin%27s_conjecture_on_primitive_roots">Artin's conjecture on primitive roots</a>
%o (PARI) forprime(p=3, 7000, if(znorder(Mod(2, p))==(p-1) && p%7==1, print1(p, ", ")))
%Y Cf. A001122, A005596, A000720.
%Y Primes p such that 2 is a primitive root modulo p and that p == 1 (mod q): A307627 (q=3), A307628 (q=5), this sequence (q=7), A323577 (q=11), A323590 (q=13).
%K nonn
%O 1,1
%A _Jianing Song_, Aug 30 2019
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