Fatto matematico: 6840 is the number of ways to place 2 non-attacking kings on a 11×11 chessboard.
Trivia: 6840 is an uninteresting number.
Data storica: September 22nd is the day in 1789 that Battle of Rymnik establishes Alexander Suvorov as a pre-eminent Russian military commander after his allied army defeat superior Ottoman Empire forces.