A262932 Numbers k such that 7 is a square mod k.

1, 2, 3, 6, 7, 9, 14, 18, 19, 21, 27, 29, 31, 37, 38, 42, 47, 53, 54, 57, 58, 59, 62, 63, 74, 81, 83, 87, 93, 94, 103, 106, 109, 111, 113, 114, 118, 126, 131, 133, 137, 139, 141, 149, 159, 162, 166, 167, 171, 174, 177, 186, 189, 193, 197, 199, 203, 206, 217, 218, 222

Offset: 1

Author

Erik Pelttari, Oct 04 2015

Keywords

• nonn
• easy

Examples

			7^2 == 7 (mod 14), so 14 is a term.
5^2 == 7 (mod 18) and 13^2 == 7 (mod 18), so 18 is a term.
		

Links

• Alois P. Heinz, Table of n, a(n) for n = 1..20000

Crossrefs

Cf. A057125, A057126, A057762, A262931.

Programs

Magma

[n: n in [1..300] | exists(t){x : x in ResidueClassRing(n) | x^2 eq 7}]; // Vincenzo Librandi, Oct 05 2015

Maple

with(numtheory):
a:= proc(n) option remember; local k;
      for k from 1+`if`(n=1, 0, a(n-1))
      while mroot(7, 2, k)=FAIL do od; k
    end:
seq(a(n), n=1..80);  # Alois P. Heinz, Feb 24 2017

Mathematica

Join[{1}, Table[If[Reduce[x^2 == 7, Modulus->n] === False, Null, n], {n, 2, 300}]//Union] (* Vincenzo Librandi, Oct 05 2015 *)

PARI

for(n=1, 300, if (issquare(Mod(7, n)), print1(n", "))); \\ Altug Alkan, Oct 04 2015