[OS X TeX] Integer Calculations?

[Christopher Allen]

Sorry this isn't specific to MacOS. Does anyone remember the package  
that lets you do integer mathematics within LaTeX? I'm usually pretty  
good with Google, but I'm not finding it. I just realized I can solve  
a problem I've been having by using it, but I don't have what I was  
playing around with on my new computer, and I'm trying to get this  
fixed in the next hour if possible.

Thanks!
Chris