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A262932
Numbers k such that 7 is a square mod k.
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
OFFSET
1,2
LINKS
EXAMPLE
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.
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
KEYWORD
nonn,easy
AUTHOR
Erik Pelttari, Oct 04 2015
STATUS
approved