Happy 12/13/14! Assuming you’re living in a part of the world that formats dates in mm/dd/yy format, of course. It’s the last sequential day in this century—you’ll have to wait until the next 01/02/03 for the next cycle to start.
Fortunately, though, there are other fun mathematical dates that will happen sooner than that. Victoria Jaggard of Smithsonian.com shares a few options: primes, Mersenne primes, Fibonacci numbers, and more. Enjoy!