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%I #20 Sep 08 2022 08:44:58
%S 2,7,23,47,73,79,89,103,113,127,151,167,199,223,233,239,257,263,337,
%T 353,359,367,383,431,439,463,479,487,503,577,593,599,607,617,647,719,
%U 727,743,823,839,863,887,911,919,937,967,983,1033,1039,1049,1063,1087
%N Primes p such that x^20 = 2 has a solution mod p.
%C Complement of A059309 relative to A000040. - _Vincenzo Librandi_, Sep 13 2012
%H R. J. Mathar, <a href="/A049552/b049552.txt">Table of n, a(n) for n = 1..1000</a>
%H <a href="/index/Pri#smp">Index entries for related sequences</a>
%t ok[p_]:= Reduce[Mod[x^20 - 2, p] == 0, x, Integers] =!= False; Select[Prime[Range[200]], ok] (* _Vincenzo Librandi_, Sep 13 2012 *)
%o (Magma) [p: p in PrimesUpTo(1100) | exists(t){x : x in ResidueClassRing(p) | x^20 eq 2}]; // _Vincenzo Librandi_, Sep 13 2012
%Y Cf. A000040, A059309.
%K nonn,easy
%O 1,1
%A _N. J. A. Sloane_