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A262932 Numbers n such that 7 is a square mod n. 2
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

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

EXAMPLE

7^2==7 (mod 14), so 14 is a member.

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

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 *)

PROG

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

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

CROSSREFS

Cf. A057125, A057126, A057762, A262931.

Sequence in context: A177729 A049993 A167793 * A018423 A018700 A018295

Adjacent sequences:  A262929 A262930 A262931 * A262933 A262934 A262935

KEYWORD

nonn,easy

AUTHOR

Erik Pelttari, Oct 04 2015

STATUS

approved

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Last modified May 30 06:51 EDT 2017. Contains 287302 sequences.