A216862 - OEIS

%I #5 Sep 08 2022 08:46:03

%S 2,3,5,7,13,17,19,23,29,37,43,47,53,59,67,71,73,79,83,89,97,103,107,

%T 109,113,127,137,139,149,157,163,167,173,179,193,197,199,223,227,229,

%U 233,239,251,257,263,269,277,283,293,307,311,313,317,337,347,349,353,359,367,373,379

%N Primes p such that x^5 = 20 has a solution mod p.

%C Complement of A040985 relative to A000040.

%H Vincenzo Librandi, <a href="/A216862/b216862.txt">Table of n, a(n) for n = 1..1000</a>

%t ok[p_]:=Reduce[Mod[x^5-20,p]==0,x,Integers]=!=False;Select[Prime[Range[150]],ok]

%o (Magma) [p: p in PrimesUpTo(400) | exists(t){x : x in ResidueClassRing(p) | x^5 eq 20}];

%K nonn,easy

%O 1,1

%A _Vincenzo Librandi_, Sep 19 2012