Fait mathématique: 21730 is an uninteresting number.
Culture générale: 21730 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Date historique: June 29th is the day in 1644 that Charles I of England defeats a Parliamentarian detachment at the Battle of Cropredy Bridge, the last battle won by an English King on English soil.