Fait mathématique: 6745 is the maximum value of n so that there exist 4 denominations of stamps so that every postage from 1 to n can be paid for with at most 25 stamps.
Culture générale: 6745 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Date historique: June 19th is the day in 1910 that the first Father's Day is celebrated in Spokane, Washington.