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%I #9 Sep 08 2022 08:46:03
%S 2,3,5,7,11,13,17,19,23,31,37,41,47,53,59,61,67,71,73,79,83,89,97,101,
%T 103,107,109,131,137,139,149,151,157,163,167,173,179,181,191,193,199,
%U 223,227,229,233,241,251,257,263,269,271,277,283,293,307,311,313
%N Primes p such that x^7 = 5 has a solution mod p.
%C Complement of A042973 relative to A000040.
%H Vincenzo Librandi, <a href="/A216882/b216882.txt">Table of n, a(n) for n = 1..1000</a>
%t ok[p_] := Reduce[Mod[x^7 - 5, p] == 0, x, Integers] =!= False; Select[Prime[Range[250]], ok]
%o (Magma) [p: p in PrimesUpTo(500) | exists(t){x: x in ResidueClassRing(p) | x^7 eq 5}];
%K nonn,easy
%O 1,1
%A _Vincenzo Librandi_, Sep 19 2012
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