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%I #10 Jun 26 2022 23:37:41
%S 29,43,71,113,127,197,211,239,281,337,379,421,449,463,491,547,617,631,
%T 659,673,701,743,827,911,953,967,1009,1051,1093,1163,1303,1373,1429,
%U 1471,1499,1667,1709,1723,1933,2003,2017,2087,2129,2143
%N Primes p such that x^7 = 3 has no solution mod p.
%C Complement of A216881 relative to A000040. - _Vincenzo Librandi_, Sep 19 2012
%H Vincenzo Librandi, <a href="/A042969/b042969.txt">Table of n, a(n) for n = 1..1000</a>
%t ok[p_]:= Reduce[Mod[x^7 - 3, p] == 0, x, Integers] == False; Select[Prime[Range[800]], ok] (* _Vincenzo Librandi_, Sep 19 2012 *)
%o (Magma) [p: p in PrimesUpTo(2500) | not exists{x : x in ResidueClassRing(p) | x^7 eq 3} ]; // _Vincenzo Librandi_, Sep 19 2012
%K nonn,easy
%O 1,1
%A _N. J. A. Sloane_
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