Fatto matematico: 83539 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Trivia: 83539 is an unremarkable number.
Data storica: September 20th is the day in 1378 that Cardinal Robert of Geneva, called by some the Butcher of Cesena, is elected as Avignon Pope Clement VII, beginning the Papal schism.