PagesPerScreen defines the number of links in search result navigator.
The default search result page navigator (usually displayed in the bottom of search HTML output) contains a link to the previous result page, a link to the next result page, and PagesPerScreen links to the other pages in between, with the current page being in the middle:
<< Prev 1 2 3 4 5 [6] 7 8 9 10 Next >>
The default value is 10.