Fatto generale: 21563 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 21563 is a boring number.
Trivia: 21563 is an unremarkable number.
Data storica: January 13th is the day in 1966 that Robert C. Weaver becomes the first African American Cabinet member when he is appointed United States Secretary of Housing and Urban Development.