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Denumerably infinite

If you can assign a unique positive integer to every element of an infinit set, it is called countably infinite.

 


Explanation

The set of natural numbers is countably infinite. But also the set of integers is countable, something you might not expect, because

Natural numbers 0 , 1 , 2 , 3 , 4 , ...
Integers ... , –4 , –3 , –2 , –1 , 0 , 1 , 2 , 3 , 4 , ...

The amount of integers is twice the amount of natural numbers, because at every positive integer there is a corresponding negative integer. Infinity is not a number, and you notice that here.

 


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