Mathematical fact: 7894 is a value of n for which n and 8n together use each digit 1-9 exactly once.
Trivia: 7894 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Historical date: August 11th is the day in 1982 that a bomb explodes on Pan Am Flight 830, en route from Tokyo to Honolulu, killing one teenager and injuring 15 passengers.