Chapter R - Section R.1 - Factors and the Least Common Multiple - Exercise Set - Page R-6: 9

Factors: $1$ and $19$

Begin with the number $1$. Divide $19$ by $1$. The result is $19$. $19=1\cdot 19$ $1$ and $19$ are factors of $19$. Since $1$ and $19$ (the number itself) are the only factors, the number $19$ is a prime number. The factors of $19$ are $1$ and $19$.