Fatto generale: 21215 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 21215 is a boring number.
Trivia: 21215 is an uninteresting number.
Data storica: January 30th is the day in 1982 that Richard Skrenta writes the first PC virus code, which is 400 lines long and disguised as an Apple boot program called "Elk Cloner".