Fatto generale: 6424 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 6424 is the number of minimal covers of a set containing 6 elements.
Trivia: 6424 is an unremarkable number.
Data storica: August 2nd is the day in 1980 that a bomb explodes at the railway station in Bologna, Italy, killing 85 people and wounding more than 200.