Fatto generale: 21587 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 21587 is a boring number.
Trivia: 21587 is a boring number.
Data storica: February 6th is the day in 1900 that the international arbitration court at The Hague is created when the Senate of the Netherlands ratifies an 1899 peace conference decree.