# Topology on N

1. Sep 4, 2008

### nikki.arm

Hi...I'm new to the forum but I need help with the following question.

I need to find a topology on N for which there are exactly k limit points. k is a positive integer.

Tips I have received: find countable subsets in R...then a bijection will produce the needed topology on N?

Any help is greatly appreciated.

2. Sep 5, 2008

### morphism

I'm not sure I understand your question. What does it mean for a topology to only have k limit points?

Presumably N is the set of natural numbers. Are you trying to consider N as a free-standing topological space, or are you trying to topologize R, and then give N the subspace topology?

3. Sep 7, 2008

### gel

Are you trying to find http://en.wikipedia.org/wiki/Compactification_%28mathematics%29" [Broken] of N by adding k points at infinity?

You can split N into k identical copies, according to their remainders under division by k (modulo k) and add one point at infinity for each of these equivalence classes.

Last edited by a moderator: May 3, 2017