Legendre symbol
= Legendre symbol
{c}
{wiki}
For an odd prime $p$,
$$
\left(\frac ap\right)=
\begin{cases}
0,&p\mid a,\\
1,&a\not\equiv0\pmod p\text{ is a square},\\
-1,&a\text{ is a nonsquare}.
\end{cases}
$$
= Legendre symbol
{c}
{wiki}
For an odd prime $p$,
$$
\left(\frac ap\right)=
\begin{cases}
0,&p\mid a,\\
1,&a\not\equiv0\pmod p\text{ is a square},\\
-1,&a\text{ is a nonsquare}.
\end{cases}
$$