A028732 Nonsquares mod 19.

2, 3, 8, 10, 12, 13, 14, 15, 18

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• fini
• full

Examples

			Since 10 is not a perfect square, and there are no solutions in integers to x^2 = 10 mod 19, 10 is in the sequence.
Although 11 is not a perfect square either, there are solutions in integers to x^2 = 11 mod 19, such as x = 7, x = 12. Hence 11 is not in the sequence.
		

Programs

Mathematica

Select[Range[18], JacobiSymbol[#, 19] != 1 &] (* Alonso del Arte, Nov 19 2019 *)

Scala

val squaresMod19 = (0 to 18).map(n => n * n).map(_ % 19)
(0 to 18).diff(squaresMod19) // Alonso del Arte, Nov 19 2019