General fact: 620 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Mathematical fact: 620 is the number of sided 7-hexes.
Trivia: 620 is an unremarkable number.
Historical date: September 11th is the day in 1932 that Franciszek Żwirko and Stanisław Wigura, Polish Challenge 1932 winners, are killed when their RWD 6 airplane crashes during a storm.