Fait mathématique: 23640 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Culture générale: 23640 is an uninteresting number.
Date historique: September 20th is the day in 1519 that Ferdinand Magellan sets sail from Sanlúcar de Barrameda with about 270 men on his expedition to circumnavigate the globe.