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I stumbled upon a wikimedia picture and I saw something that I have not seen before: a CFM56 with a toothed engine exhaust. Can someone explain to me what engine variant that is?

Source Author: Konstantin Nikiforov CC-BY-SA-3.0

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”

So far my suspicion is that this is the /p option in "CFM International CFM56-5B3/P" as found when I looked up VP-BWN (the aircraft in your picture).
The useful chart at Wikipedia, as linked by @Mike-Sowsun, does not list the /P option, which would of course complicate the chart. I wonder how many of these minor options are available? Not like I'm in the market.

More Info:
Airliners.net was excited about this roughly ten years ago, but the links to explanations have gone dry. So I was happy to see that one intrepid commenter there had done the right thing and produced a quote from the linked material, which I will reproduce here:

As stated in the article :
http://www.airbus.com/store/mm_repos...dia_object_file_FAST37_p19_p22.pdf

The "noise package" is now standard on the A321 and an option on the
other models. The reason behind this is that the A321 (heavy weight
version) doesn't comply with the new stage 4 noise limits in effect
for all new aircraft, certified after 1 January 2007. In fact this is
the present noise standard, although legally not valid for the present
A320 generation of aircraft, all certified before 1 januari 2007. All
other sub types of the A320 series are at or below the stage 4 noise
standard and don't need the chevrons, but can be delivered as an
option with this "noise package", to become even more silent.

Also stated in the article is the fact that the FADEC needs some
tweaking to produce the same thrust level, so there must be a loss in
efficiency somewhere. Because this is an Airbus brochure, nothing is
said about the actual loss in SFC.

Here's a similar explanation (again, without specific model number) from a 2002 GE press release:

All CFM-powered A320 family aircraft meet current FAR Stage III noise
requirements with significant margin. These engines also meet the CAEP
5 recommendations, except for the CFM56-5B-powered A321. However, CFM
and Airbus have defined an acoustic package to ensure this aircraft
will operate well within proposed limits. CFM is conducting
development testing on engine and nacelle treatments that will reduce
the cumulative noise signature at least 10 EPNdB (effective perceived
noise in decibels) below Stage III levels.

The new technology includes three-dimensional aerodynamic designed
outlet guide vanes; a core chevron nozzle; and improved reverser and
inlet linings on the nacelle. Flight tests on the A321 are scheduled
for later this year, followed by certification and entry into service
in early 2003.