Fatto generale: 84509 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 84509 is a boring number.
Trivia: 84509 is an unremarkable number.
Data storica: May 18th is the day in 1783 that First United Empire Loyalists reach Parrtown (later called Saint John), New Brunswick, Canada after leaving the United States.