(\frac{a}{p}) = \{\begin{matrix} 1 & i f a i s a q u a d r a t i c r e s i d u e m o d u l o p a n d a ≢ 0 p, \\ -1 & i f a i s a q u a d r a t i c n o n - r e s i d u e m o d u l o p, \\ 0 & i f a \equiv 0 p . \end{matrix}