Chapter R - Section R.1 - Factors and the Least Common Multiple - Exercise Set - Page R-6: 10

Factors: $1$ and $31$

Begin with the number $1$. Divide $31$ by $1$. The result is $31$. $31=1\cdot 31$ $1$ and $31$ are factors of $31$. Since $1$ and $31$ (the number itself) are the only factors, the number $31$ is a prime number. The factors of $31$ are $1$ and $31$.