First Supplement to Law of Quadratic Reciprocity/Examples/19

Examples of First Supplement to Law of Quadratic Reciprocity

 * $-1$ is a quadratic non-residue of $19$.

Proof
We have that:
 * $19 = 4 \times 5 - 1$

and so is not of the form $4 n + 1$.

The result follows from the First Supplement to Law of Quadratic Reciprocity.