Problems with permalinks

Hi,

I had my permalinks set to /%category%/%postname%/

my problem is whenever I want a page to be only titled as a number (“ex: wordpress/13.html“) it automatically converts it into wordpress?13-2.html“

It adds up with a “-2”. There are no other existing pages for this. But I specifically want the Page title to be a number, but somehow it adds a dash and a number to it. Any advice on how to solve this?

Thanks