Fatto generale: 20021 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 20021 is a boring number.
Trivia: 20021 is an unremarkable number.
Data storica: October 24th is the day in 1861 that the First Transcontinental Telegraph line across the United States is completed, spelling the end for the 18-month-old Pony Express.