OFFSET
1,1
COMMENTS
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
MATHEMATICA
ok[p_]:= Reduce[Mod[x^4 - 21, p] == 0, x, Integers] == False; Select[Prime[Range[100]], ok] (* Vincenzo Librandi, Sep 18 2012 *)
PROG
(Magma) [p: p in PrimesUpTo(500) | not exists{x : x in ResidueClassRing(p) | x^4 eq 21} ]; // Vincenzo Librandi, Sep 18 2012
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved