Definition:Polynomial Congruence/Number of Solutions

Definition
Let:
 * $P \left({x}\right) \equiv 0 \pmod n$

be a polynomial congruence.

Let $S = \left\{{b_1, b_2, \ldots, b_n}\right\}$ be a complete set of residues modulo $n$.

The number of solutions of $P \left({x}\right) \equiv 0 \pmod n$ is the number of integers $b \in S$ for which $P \left({b}\right) \equiv 0 \pmod n$.