The AR stands for "Active Area" may be just a faculae bright area with/ without visible spot.
The numbers are designated by NOAA
https://www.swpc.noaa.gov/
and updated/ shown on SpaceWeatherLive
https://www.spaceweatherlive.com/en/...unspot-regions
See also:
https://hesperia.gsfc.nasa.gov/sfthe...htm#AR_numbers