that doesnt make any sense... android is a mobile os, ie for mobile devices. raspberry pi is a barebones computer. the hardware specs will be different from whats needed. however, there might be an os like android [insert sugar item here] for raspberry pi
Pretty much, much of the software that usually runs on android probably won't work (such as the phone app).
There's also a game console (whose name has escaped me at the moment) that uses android as an OS.