Fait général: 21668 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fait mathématique: 21668 is a boring number.
Culture générale: 21668 is an uninteresting number.
Date historique: April 28th is the day in 1947 that Thor Heyerdahl and five crew mates set out from Peru on the Kon-Tiki to prove that Peruvian natives could have settled Polynesia.