Fatto generale: 766 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 766 is the number of series-reduced planted trees with 9 leaves.
Trivia: 766 is an uninteresting number.
Data storica: February 4th is the day in 960 that the coronation of Zhao Kuangyin as Emperor Taizu of Song, initiating the Song Dynasty period of China that would last more than three centuries.