%I #9 Dec 20 2019 20:45:09

%S 2,3,6,7,8,10,11,12,13,14,15,17,18,19

%N Nonsquares mod 20.

%t Complement[Range[0, 19], PowerMod[Range[20], 2, 20]] (* _Alonso del Arte_, Dec 20 2019 *)

%o (Scala) (0 to 19).diff((1 to 20).map(n => (n * n) % 20)) // _Alonso del Arte_, Dec 20 2019

%Y Cf. A010382.

%K nonn,fini,full,easy

%O 1,1

%A _N. J. A. Sloane_