Fatto generale: 18540 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 18540 is an unremarkable number.
Trivia: 18540 is an unremarkable number.
Data storica: October 4th is the day in 610 that Heraclius arrives by ship from Africa at Constantinople, overthrows Byzantine Emperor Phocas and becomes Emperor.