Let me give you example of what I mean by a long list of pages:
![List of Pages](https://i.imgur.com/2OKF6.png)

So when you click 19 it has to determine how many new pages to show and how many old pages not to show.

For example:
![List 2](https://i.imgur.com/BgZAT.png)

How many new pages should you should and how many old pages should you not show?