Fatto generale: 21871 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 21871 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Trivia: 21871 is a boring number.
Data storica: November 17th is the day in 1810 that Sweden declares war on its ally the United Kingdom to begin the Anglo-Swedish War, although no fighting ever takes place.