# What is countable?
## Natural Numbers
Quite simple
$$\mathbb{N} = \{ 1, 2, 3, 4, \dots \}$$
Which you can just add it up every time
## Integer Numbers
$Z$ can be countable as you can go
$$1 \to 0$$
$$2 \to 1$$
$$3 \to -1$$
$$4 \to 2$$
$$5 \to -2$$
and so on...

Here they start at 0, then go 1, -1, 2, -2, etc...
## Rational Numbers
They are countable, but it is a lot more work to show