Fatto generale: 21742 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 21742 is an unremarkable number.
Trivia: 21742 is an uninteresting number.
Data storica: July 11th is the day in 1804 that a duel occurs in which the Vice President of the United States Aaron Burr mortally wounds former Secretary of the Treasury Alexander Hamilton.