Fait mathématique: 8509 is a value of n for which |cos(n)| is smaller than any previous integer.
Culture générale: 8509 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Date historique: April 18th is the day in 1980 that the Republic of Zimbabwe (formerly Rhodesia) comes into being, with Canaan Banana as the country's first President.