Fatto generale: 21908 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 21908 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Trivia: 21908 is an uninteresting number.
Data storica: December 24th is the day in 1818 that the first performance of "Silent Night" takes place in the church of St. Nikolaus in Oberndorf, Austria.