Hecho matemático: 2820 is an uninteresting number.
Trivia: 2820 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fecha histórica: 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.