Fatto generale: 6411 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 6411 is a truncated cube number.
Trivia: 6411 is an unremarkable number.
Data storica: July 20th is the day in 1969 that a cease fire is announced between Honduras and El Salvador, 6 days after the beginning of the "Football War".