Fatto generale: 21037 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 21037 is an uninteresting number.
Trivia: 21037 is an uninteresting number.
Data storica: August 5th is the day in 1388 that the Battle of Otterburn, a border skirmish between the Scottish and the English in Northern England, is fought near Otterburn.