Fatto generale: 21803 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 21803 is an unremarkable number.
Trivia: 21803 is an unremarkable number.
Data storica: September 10th is the day in 1977 that Hamida Djandoubi, convicted of torture and murder, is the last person to be executed by guillotine in France.