Divison and Divisors

Definition 4.1:
For integers $a$ and $b$, we say that $a$ divides $b$, denoted $a \mid b$, if there exists an integer $c$ such that $b = ac$. In this case, $a$ is called a divisor of $b$, and $b$ is called a multiple of $a$. If $a \neq 0$ and a divisor $c$ exists, it is called the quotient when $b$ is divided by $a$, and we write $c = \frac{b}{a}$ or $c = b/a$. 4. We write $a \nmid b$ if $a$ does not divide $b$.