The M & M car is #18 and is driven by Kyle Busch.
Click on the link below to see the 2011 Nascar Cup Series drivers.
Matt Kenseth won the 2003 Winston Cup championship, driving the #17 car.
Before the #18, Kyle Busch drove the #84 car in 2004 and the #5 car from 2005-2007 for Hendrick Motorsports.
No. If Nascar did this it would mean that most numbers would be retired and we would be seeing 3 cars on the track.