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%I #9 Sep 08 2022 08:44:53
%S 2,5,11,19,29,31,59,61,71,79,131,139,151,179,191,199,211,229,239,251,
%T 271,311,331,349,359,379,401,409,419,421,431,439,449,479,491,499,509,
%U 521,569,571,599,619,631,659,661
%N Primes p such that x^4 = 20 has a solution mod p.
%H Vincenzo Librandi, <a href="/A040147/b040147.txt">Table of n, a(n) for n = 1..1000</a>
%t ok [p_]:=Reduce[Mod[x^4 - 20, p]== 0, x, Integers]=!= False; Select[Prime[Range[180]], ok] (* _Vincenzo Librandi_, Sep 12 2012 *)
%o (Magma) [p: p in PrimesUpTo(800) | exists(t){x : x in ResidueClassRing(p) | x^4 eq 20}]; // _Vincenzo Librandi_, Sep 12 2012
%Y Cf. A040148.
%K nonn,easy
%O 1,1
%A _N. J. A. Sloane_.
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