Fatto generale: 6456 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 6456 is a value of n for which the n^{th} prime begins with the digits of n.
Trivia: 6456 is an uninteresting number.
Data storica: September 3rd is the day in 1999 that an 87-automobile pile-up happens on Highway 401 freeway just East of Windsor, Ontario, Canada after an unusually thick fog from Lake St. Clair.