Fait mathématique: 1787 is the number of different arrangements (up to rotation and reflection) of 12 non-attacking queens on a 12×12 chessboard.
Culture générale: 1787 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Date historique: November 21st is the day in 1905 that Albert Einstein's paper, Does the Inertia of a Body Depend Upon Its Energy Content?, is published in the journal "Annalen der Physik".