The set Z of integers is countably infinite.

What is considered countably infinite?

A set is countably infinite if its elements can be put in one-to-one correspondence with the set of natural numbers. In other words, one can count off all elements in the set in such a way that, even though the counting will take forever, you will get to any particular element in a finite amount of time.

Is a countably infinite set countable?

is also countable. Countably infinite sets have cardinal number aleph-0. Examples of countable sets include the integers, algebraic numbers, and rational numbers.