Fatto generale: 21431 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 21431 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Trivia: 21431 is an uninteresting number.
Data storica: September 3rd is the day in 301 that San Marino, one of the smallest nations in the world and the world's oldest republic still in existence, is founded by Saint Marinus.