Fatto generale: 83909 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 83909 is a boring number.
Trivia: 83909 is an unremarkable number.
Data storica: September 25th is the day in 1555 that the Peace of Augsburg is signed in Augsburg by Charles V and the princes of the Schmalkaldic League.