Fait général: 21753 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fait mathématique: 21753 is a boring number.
Culture générale: 21753 is an unremarkable number.
Date historique: July 22nd is the day in 2002 that Israel kills Salah Shahade, the Commander-in-Chief of Hamas's military arm, the Izz ad-Din al-Qassam Brigades.