Fatto generale: 21020 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 21020 is an uninteresting number.
Trivia: 21020 is an uninteresting number.
Data storica: July 19th is the day in 1961 that Tunisia imposes a blockade on the French naval base at Bizerte; the French would capture the entire town four days later.