Fait mathématique: 6643 is the smallest number which is palindromic in bases 2 and 3.
Culture générale: 6643 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Date historique: March 9th is the day in 141 BC that Liu Che, posthumously known as Emperor Wu of Han, assumes the throne over the Han Dynasty of China.