A038878 - OEIS

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

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OFFSET

1,1

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

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 *)

CROSSREFS

Sequence in context: A218100 A349622 A078373 * A040112 A246373 A074855

Adjacent sequences: A038875 A038876 A038877 * A038879 A038880 A038881

KEYWORD

nonn

AUTHOR

N. J. A. Sloane.

STATUS

approved