Fait général: 21816 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fait mathématique: 21816 is an uninteresting number.
Culture générale: 21816 is a boring number.
Date historique: September 23rd is the day in 1959 that the MS Princess of Tasmania, Australia’s first passenger roll-on/roll-off diesel ferry, makes her maiden voyage across Bass Strait.