Fatto matematico: 6820 is the number of regions formed when all diagonals are drawn in a regular 23-gon.
Trivia: 6820 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Data storica: September 2nd is the day in 1666 that the Great Fire of London breaks out and burns for three days, destroying 10,000 buildings including St Paul's Cathedral.