Fatto generale: 7776 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 7776 is a 5^{th} power whose digits are non-increasing.
Trivia: 7776 is a boring number.
Data storica: April 15th is the day in 1958 that Walter O'Malley's Los Angeles Dodgers host the first Major League Baseball game played on the West Coast of the United States.