Fatto generale: 21712 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 21712 is an uninteresting number.
Trivia: 21712 is a boring number.
Data storica: June 11th is the day in 1892 that the Limelight Department, one of the world's first film studios, is officially established in Melbourne, Australia.