Fait mathématique: 2782 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 19 stamps.
Culture générale: 2782 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Date historique: August 13th is the day in 1521 that Tenochtitlán (present day Mexico City) falls to conquistador Hernán Cortés.