Dealing with pages can get trickier if you allow the user to change the number displayed per page when not on the first page. It's not particularly hard to figure out, but what the right thing to do when the boundaries don't line up is a question that needs to be answered, as well, as well as dealing with user confusion about what page they are then on. Dealing with number ranges instead of pages solves these problems, at the cost of some readability.