Fatto matematico: 2820 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Trivia: 2820 is a boring number.
Data storica: September 20th is the day in 1697 that the Treaty of Rijswijk is signed by France, England, Spain, the Holy Roman Empire and the Dutch Republic ending the Nine Years' War (1688–97).