Fatto generale: 20718 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 20718 is an uninteresting number.
Trivia: 20718 is an uninteresting number.
Data storica: September 20th is the day in 1378 that Cardinal Robert of Geneva, called by some the Butcher of Cesena, is elected as Avignon Pope Clement VII, beginning the Papal schism.