Fatto generale: 6440 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 6440 is a value of n for which n!!!!.
Trivia: 6440 is an uninteresting number.
Data storica: August 18th is the day in 1977 that Steve Biko is arrested at a police roadblock under the Terrorism Act No 83 of 1967 in King William's Town, South Africa.