Fatto generale: 21081 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 21081 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Trivia: 21081 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Data storica: September 18th is the day in 324 that Constantine the Great decisively defeats Licinius in the Battle of Chrysopolis, establishing Constantine's sole control over the Roman Empire.