Hecho general: 6440 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Hecho matemático: 6440 is a value of n for which n!!!!.
Trivia: 6440 is an unremarkable number.
Fecha histórica: August 18th is the day in 1983 that Hurricane Alicia hits the Texas coast, killing 22 people and causing over USD $1 billion in damage (1983 dollars).