Fait mathématique: 1842 is the number of rooted trees with 11 vertices.
Culture générale: 1842 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Date historique: January 15th is the day in 1947 that the brutalized corpse of Elizabeth Short ("The Black Dahlia") is found in Leimert Park, Los Angeles.