General fact: 21671 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Mathematical fact: 21671 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Trivia: 21671 is an unremarkable number.
Historical date: May 1st is the day in 1576 that Stefan Batory, the reigning Prince of Transylvania, marries Anna Jagiellon and they become the co-rulers of the Polish-Lithuanian Commonwealth.