Rap song needed for project?

I am trying to do a project with my math students where we rewrite a rap song about math and create a video. My students keep giving me songs that they like, but I can't use them even if we rewrite them because the original is so inappropriate. The songs don't have to be perfectly clean, but they need to be somewhat decent. The more appropriate songs tend to be love songs, and they don't have quite the beat that I'm looking for.

Are there any rap or hip hop songs out there that have a good beat with okay lyrics that could be parodied into a catchy song? My inspiration comes from the videos from Westerville South High School -- you can find them on youtube.

I would appreciate any ideas. Thanks!