Fatto matematico: 6840 is the number of ways to place 2 non-attacking kings on a 11×11 chessboard.
Trivia: 6840 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Data storica: September 22nd is the day in 1995 that Nagerkovil school bombing, is carried out by Sri Lankan Air Force in which at least 34 die, most of them ethnic Tamil school children.