# Is coutnable unions of finite sets an infinite set? (1 Viewer)

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#### MrGandalf

Hiya. :)

While doing an assignment I ran into this little problem.

We are working in the set of natural numbers $$\mathbb{N}$$.

If i collect each natural number in a set
$$S_1 = \{1\}, S_2 = \{2\},\ldots, S_n = \{n\},\ldots$$

What happens when I take the countable union of all these?
$$S = \bigcup_{i\in\mathbb{N}}S_i$$

The resulting set will be an infinite set, right? It will be equal to $$\mathbb{N}$$?

#### CRGreathouse

Homework Helper
The resulting set will be an infinite set, right? It will be equal to $$\mathbb{N}$$?
Right. What's the problem?

#### Cexy

Yup.

Finite unions of finite sets are finite.

Countable unions of finite sets are countable.

Finite unions of countable sets are countable.

Countable unions of countable sets are countable.

#### MrGandalf

Thanks.

I was just really unsure there for a moment, but I think I see it now.
Thanks for clearing that up for me.

PS Sorry about the typo in the thread title.

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