Fatto generale: 21291 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 21291 is a boring number.
Trivia: 21291 is a boring number.
Data storica: April 16th is the day in 1945 that the Red Army begins the final assault on German forces around Berlin, with nearly one million troops fighting in the Battle of the Seelow Heights.