Fatto generale: 90721 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 90721 is a boring number.
Trivia: 90721 is an unremarkable number.
Data storica: May 20th is the day in 1813 that Napoleon Bonaparte leads his French troops into the Battle of Bautzen in Saxony, Germany, against the combined armies of Russia and Prussia.