You know those people who turn their birthday into a birthweek? Justin Bieber is one of those people.

TMZ just posted a video of the singer celebrating his 21st birthday at Omnia Nightclub in Las Vegas on Saturday (Mar. 14). In the video, JB hops up on the DJ booth and starts singing "Happy Birthday" to himself -- oh, and he gives a special shoutout to manager Scooter Braun, too.

Did I mention that Justin Bieber's actual 21st birthday was on March 1? Because Justin Bieber's actual 21st birthday was on March 1.

As in literally two weeks ago.

Which would make this a birthfortnight.