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A038883 Odd primes p such that 13 is a square mod p. 45
3, 13, 17, 23, 29, 43, 53, 61, 79, 101, 103, 107, 113, 127, 131, 139, 157, 173, 179, 181, 191, 199, 211, 233, 251, 257, 263, 269, 277, 283, 311, 313, 337, 347, 367, 373, 389, 419, 433, 439, 443, 467, 491, 503, 521, 523, 547, 563, 569, 571, 599, 601, 607, 641 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Equivalently, by quadratic reciprocity (since 13 == 1 mod 4), primes p which are squares mod 13.

The squares mod 13 are 0, 1, 4, 9, 3, 12 and 10.

Also primes of the form x^2 + 3*x*y - y^2. Discriminant = 13. Class = 1. This was originally a separate entry, submitted by Laura Caballero Fernandez, Lourdes Calvo Moguer, Maria Josefa Cano Marquez, Oscar Jesus Falcon Ganfornina and Sergio Garrido Morales (oscfalgan(AT)yahoo.es), Jun 06 2008. R. J. Mathar proved that this coincides with the present sequence, Jul 22 2008

Primes p such that x^2 + x = 3 has a solution mod p (the solutions over the reals are (-1+-sqrt(13))/2).  [Joerg Arndt, Jul 27 2011]

REFERENCES

Z. I. Borevich and I. R. Shafarevich, Number Theory.

D. B. Zagier, Zetafunktionen und quadratische Koerper.

LINKS

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

Peter Luschny, Binary Quadratic Forms

N. J. A. Sloane et al., Binary Quadratic Forms and OEIS (Index to related sequences, programs, references)

EXAMPLE

13 == 1 mod 3 and 1 is a square, so 3 is on the list.

101 is prime and congruent to 7^2 = 49 == 10 (mod 13), so 101 is on the list.

MATHEMATICA

Select[ Prime@ Range@ 118, JacobiSymbol[ #, 13] > -1 &] (* Robert G. Wilson v, May 16 2008 *)

Select[Flatten[Table[13n + {1, 3, 4, 9, 10, 12}, {n, 50}]], PrimeQ[#] &] (* Alonso del Arte, Sep 16 2012 *)

PROG

(PARI) forprime(p=3, 1e3, if(issquare(Mod(13, p)), print1(p", "))) \\ Charles R Greathouse IV, Jul 15 2011

(Sage) # uses[binaryQF]

# The function binaryQF is defined in the link 'Binary Quadratic Forms'.

Q = binaryQF([1, 3, -1])

print(Q.represented_positives(641, 'prime')) # Peter Luschny, Sep 20 2018

CROSSREFS

Cf. A038872 (d=5). A038873 (d=8). A068228, A141123 (d=12). A038883 (primes p such that d=13 is a square mod p). A038889 (d=17). A141111, A141112 (d=65).

Cf. A296937.

For a list of sequences giving numbers and/or primes represented by binary quadratic forms, see the "Binary Quadratic Forms and OEIS" link.

Sequence in context: A309291 A040123 A296936 * A141188 A019347 A184777

Adjacent sequences:  A038880 A038881 A038882 * A038884 A038885 A038886

KEYWORD

nonn

AUTHOR

N. J. A. Sloane

EXTENSIONS

Edited by N. J. A. Sloane, Apr 27 2008, Jul 28 2008

STATUS

approved

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Last modified July 14 13:27 EDT 2020. Contains 335729 sequences. (Running on oeis4.)