A262931 - OEIS

%I #31 Sep 08 2022 08:46:14

%S 1,2,3,5,6,10,15,19,23,25,29,30,38,43,46,47,50,53,57,58,67,69,71,73,

%T 75,86,87,94,95,97,101,106,114,115,125,129,134,138,139,141,142,145,

%U 146,149,150,159,163,167,173,174,190,191,193,194,197,201,202,211,213

%N Numbers k such that 6 is a square mod k.

%H Alois P. Heinz, <a href="/A262931/b262931.txt">Table of n, a(n) for n = 1..20000</a>

%e 6^2 == 6 (mod 15), so 15 is a term.

%p with(numtheory):

%p a:= proc(n) option remember; local k;

%p       for k from 1+`if`(n=1, 0, a(n-1))

%p       while mroot(6, 2, k)=FAIL do od; k

%p     end:

%p seq(a(n), n=1..80);  # _Alois P. Heinz_, Feb 24 2017

%t Join[{1}, Table[If[Reduce[x^2 == 6, Modulus->n] === False, Null, n], {n, 2, 300}]//Union] (* _Vincenzo Librandi_, Oct 05 2015 *)

%o (PARI) for(n=1, 300, if (issquare(Mod(6, n)), print1(n", "))); \\ _Altug Alkan_, Oct 04 2015

%o (Magma) [n: n in [1..300] | exists(t){x : x in ResidueClassRing(n) | x^2 eq 6}]; // _Vincenzo Librandi_, Oct 05 2015

%Y Cf. A057125, A057126, A057762, A262932.

%K nonn,easy

%O 1,2

%A _Erik Pelttari_, Oct 04 2015