Fatto generale: 21637 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 21637 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Trivia: 21637 is an uninteresting number.
Data storica: March 28th is the day in 1910 that Henri Fabre becomes the first person to fly a seaplane, the Fabre Hydravion, after taking off from a water runway near Martigues, France.