What is that CFM56 with a toothed exhaust on an A321?
The “toothed” exhaust are called Chevrons and they reduce noise. They are an option on CFM56 equipped A321 aircraft. 

Wikipedia CFM International CFM56 

”GE and Snecma also tested the effectiveness of chevrons on reducing jet noise. After examining configurations in the wind tunnel, CFMI chose to flight-test chevrons built into the core exhaust nozzle. The chevrons reduced jet noise by 1.3 perceived loudness decibels during takeoff conditions, and are now offered as an option with the CFM56 for the Airbus A321”