Fait général: 6840 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fait mathématique: 6840 is the number of ways to place 2 non-attacking kings on a 11×11 chessboard.
Culture générale: 6840 is an unremarkable number.
Date historique: September 22nd is the day in 1975 that Sara Jane Moore tries to assassinate U.S. President Gerald Ford, but is foiled by Oliver Sipple.