Fait général: 8439 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fait mathématique: 8439 is a value of n for which n and 8n together use each digit 1-9 exactly once.
Culture générale: 8439 is an uninteresting number.
Date historique: February 7th is the day in 1301 that Edward of Caernarvon (later King Edward II of England) becomes the first English Prince of Wales.