A038894 Primes p such that 21 is not a square mod p.

2, 11, 13, 19, 23, 29, 31, 53, 61, 71, 73, 97, 103, 107, 113, 137, 139, 149, 157, 179, 181, 191, 197, 199, 223, 229, 233, 239, 241, 263, 271, 281, 283, 307, 313, 317, 347, 349, 359, 367, 389, 397, 401, 409, 431, 433, 439, 443, 449, 491, 523, 557, 569, 577, 599, 601

Offset

1,1

Comments

Primes p such that 1+5*x+x^2 is irreducible over GF(p). - Joerg Arndt, Jul 19 2012

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Mathematica

Select[Prime@Range[120], JacobiSymbol[21, #] == -1 &] (* Vincenzo Librandi, Sep 08 2012 *)

Prog

(PARI) is(n)=!issquare(21, n) && isprime(n) \\ Charles R Greathouse IV, Nov 21 2014

Crossrefs

Sequence in context: A068807 A241732 A154812 * A207039 A095743 A106984

Adjacent sequences: A038891 A038892 A038893 * A038895 A038896 A038897

Keyword

nonn

Author

N. J. A. Sloane.

Status

approved