Fatto matematico: 7746 is the number permutations of {1,2,3,...,21} where adjacent numbers differ by no more than 2.
Trivia: 7746 is an unremarkable number.
Data storica: March 16th is the day in 455 that Emperor Valentinian III is assassinated by two Hunnic retainers while training with the bow on the Campus Martius (Rome).