## Thinking Mathematically (6th Edition)

$0$ (Refer to the step by step part for the explanation).
RECALL: The integers are: $\left\{...-3, -2, -1, 0, 1, 2, 3, ...\right\}$ The natural numbers are: $\left\{1, 2, 3, ...\right\}$ Thus, an example of an integer that is not a natural number is $0$. (There are a lot of other examples such as -1, -2, -3, etc.)