%I #8 Sep 08 2022 08:44:53

%S 2,3,7,11,13,19,23,31,37,43,47,59,61,67,71,73,79,83,97,103,107,109,

%T 127,131,139,151,157,163,167,179,181,191,193,199,211,223,227,229,239,

%U 241,251,263,271,277,283,307,311

%N Primes p such that x^4 = 9 has a solution mod p.

%H Vincenzo Librandi, <a href="/A040116/b040116.txt">Table of n, a(n) for n = 1..1000</a>

%t ok [p_]:=Reduce[Mod[x^4 - 9, p]== 0, x, Integers]=!= False; Select[Prime[Range[170]], ok] (* _Vincenzo Librandi_, Sep 12 2012 *)

%o (Magma) [p: p in PrimesUpTo(400) | exists(t){x : x in ResidueClassRing(p) | x^4 eq 9}]; // _Vincenzo Librandi_, Sep 12 2012

%K nonn,easy

%O 1,1

%A _N. J. A. Sloane_.