A028773 - OEIS

%I #12 Jan 04 2020 02:56:23

%S 2,3,5,6,7,8,10,11,12,13,14,15,17,18,19,20,22,23,26,27,28,29,30,31,32,

%T 33,34,35,37,38,39,41,42,43,44,46,47,48,50,51,52,53,54,55,56,57,58,59

%N Nonsquares mod 60.

%e x^2 = 20 mod 60 has no solutions, so 20 is in the sequence.

%e x^2 = 21 mod 60 has the following solutions: x = 9, x = 21, x = 39, x = 51. Hence 21 is not in the sequence.

%t Complement[Range[59], PowerMod[Range[60], 2, 60]] (* _Alonso del Arte_, Jan 13 2017 *)

%o (Scala) (0 to 59).diff((1 to 60).map(n => n * n % 60)) // _Alonso del Arte_, Jan 03 2020

%Y Cf. A010421.

%K nonn,fini,full,easy

%O 1,1

%A _N. J. A. Sloane_