%I #10 Feb 24 2023 03:11:13
%S 4,5,6,8,10,12,13,14,15,16,17,18,20,21,22,24,25,26,28,29,30,32,33,34,
%T 35,36,37,38,39,40,41,42,44,45,46,48,50,51,52,53,54,55,56,57,58,60,61,
%U 62,63,64,65,66,68,69,70,72,73,74,75,76,77,78,80,82,84,85
%N Numbers n such that x^2 = 1 has more than two solutions in the Gaussian integers modulo n.
%e 13 is in the sequence because 5i, 8i, 1 and 12 are solutions of x^2 = 1 (mod 13).
%t h[n_] := Flatten[Table[a + b I, {a, 0, n - 1}, {b, 0, n - 1}]]; sol[n_] := Select[h[n], Mod[#^2, n] == 1 &]; Select[Range[100], Length[sol[#]] > 2 &]
%K nonn
%O 1,1
%A _José María Grau Ribas_, Jun 16 2013