When you look up a user on the site and then click on the link to their Blog there are prev and next arrows with 9 numbers in between. The links when you click on the next link or any of the numbers returns a 404 error.
Here is a page where you can try this:
https://www.drcarney.com/kenscircus/170-blog
Scroll to the bottom and then click on one of the numbers to see the 404 error page.
Thanks, Sean