Fait mathématique: 21640 is an unremarkable number.
Culture générale: 21640 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Date historique: March 31st is the day in 1492 that Queen Isabella of Castille issues the Alhambra decree, ordering her 150,000 Jewish subjects to convert to Christianity or face expulsion.