%I #10 Sep 08 2022 08:45:03
%S 433,919,1423,1999,2017,2143,2287,2791,2953,3457,3889,4177,4519,4663,
%T 5113,5167,6679,6967,8713,9631,9649,9721,10009,11863,12241,12583,
%U 12799,13177,13591,15913,16057,16111,16561,16921,17551,18127,18793,19081
%N Primes p such that x^18 = 2 has no solution mod p, but x^6 = 2 has a solution mod p.
%H Vincenzo Librandi, <a href="/A059664/b059664.txt">Table of n, a(n) for n = 1..340</a>
%t Select[Prime[Range[PrimePi[20000]]], !MemberQ[PowerMod[Range[#], 18, #], Mod[2, #]] && MemberQ[PowerMod[Range[#], 6, #], Mod[2, #]]&] (* _Vincenzo Librandi_, Sep 21 2013 *)
%o (Magma) [p: p in PrimesUpTo(20000) | not exists{x: x in ResidueClassRing(p) | x^18 eq 2} and exists{x: x in ResidueClassRing(p) | x^6 eq 2}]; // _Vincenzo Librandi_, Sep 21 2012
%Y A000040, A040992, A040993, A049550, A059665.
%K nonn,easy
%O 1,1
%A _Klaus Brockhaus_, Feb 04 2001