A028732 Nonsquares mod 19.

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

Offset

1,1

Links

Table of n, a(n) for n=1..9.

Example

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.

Mathematica

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

Prog

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

Crossrefs

Sequence in context: A005454 A119187 A008522 * A028751 A325424 A057543

Adjacent sequences: A028729 A028730 A028731 * A028733 A028734 A028735

Keyword

nonn,fini,full

Author

N. J. A. Sloane

Status

approved