[Mediawiki-l] Huge output in Site statistics

[sakura.i8i at gmail.com]

I was looking at our site statistics but I was surprised with the result.

Its says:
---
There are *1,542,401* total pages in the database. This includes "talk"
pages, pages about Wikology, minimal "stub" pages, redirects, and others
that probably don't qualify as content pages. Excluding those, there are *
18,446,744,073,709,551,615* pages that are probably legitimate content
pages.

There have been a total of *26,075* page views, and *592* page edits since
the wiki was setup. That comes to *0.00* average edits per page, and
*44.05*views per edit.
---

The total pages is quite accurate but I wonder where
*18,446,744,073,709,551,615
*came? I tried to look at the codes and google but i cant find any
explanation of such huge number. Can anyone tell me?