A038878 Primes p such that 7 is a square mod p.

2, 3, 7, 19, 29, 31, 37, 47, 53, 59, 83, 103, 109, 113, 131, 137, 139, 149, 167, 193, 197, 199, 223, 227, 233, 251, 271, 277, 281, 283, 307, 311, 317, 337, 367, 373, 383, 389, 401, 419, 421, 439, 449, 457, 467

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn

Comments

Also, only entries p=1 (mod 4) of the sequence are squares mod 7 (from the quadratic reciprocity law). - Lekraj Beedassy, Jul 21 2004

2 and 7 together with primes congruent to +/- {1, 3, 9} mod 28. - Eric M. Schmidt, Jan 24 2014

Least numbers m such that 7+m*a(n) is a square: 1, 3, 6, 3, 1, 3, 2, 6, 9, 6, 3, 6, 2, 9, 3, 1, ... - Zak Seidov, Sep 25 2014

Links

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

Programs

Mathematica

Select[Prime[Range[100]], JacobiSymbol[7, #] != -1 &] (* Vincenzo Librandi, Sep 07 2012 *)
Union[{2,7},Select[Flatten[Table[{1,3,9,19,25,27}+28*k,{k,0,10}]],PrimeQ]](* Zak Seidov, Sep 25 2014 *)