A049553 - OEIS

A049553

Primes p such that x^21 = 2 has a solution mod p.

2, 3, 5, 11, 17, 23, 31, 41, 47, 53, 59, 83, 89, 101, 107, 109, 131, 137, 149, 157, 167, 173, 179, 191, 223, 227, 229, 233, 251, 257, 263, 269, 277, 283, 293, 307, 311, 317, 347, 353, 359, 383, 389, 397, 401, 419, 431, 433, 439, 443, 457, 461, 467, 479, 499

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

Complement of A059310 relative to A000040. - Vincenzo Librandi, Sep 14 2012

LINKS

R. J. Mathar, Table of n, a(n) for n = 1..1000

Index entries for related sequences

MATHEMATICA

ok[p_]:= Reduce[Mod[x^21 - 2, p] == 0, x, Integers] =!= False; Select[Prime[Range[150]], ok] (* Vincenzo Librandi, Sep 14 2012 *)

PROG

(Magma) [p: p in PrimesUpTo(500) | exists(t){x : x in ResidueClassRing(p) | x^21 eq 2}]; // Vincenzo Librandi, Sep 14 2012