Fait mathématique: 1817 is the number of polyominoes with 8 or fewer squares.
Culture générale: 1817 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Date historique: December 21st is the day in 1826 that American settlers in Nacogdoches, Mexican Texas, declare their independence, starting the Fredonian Rebellion.