Fatto generale: 5551 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 5551 is the number of trees on 17 vertices with diameter 6.
Trivia: 5551 is an unremarkable number.
Data storica: March 13th is the day in 1964 that American Kitty Genovese is murdered, reportedly in view of neighbors who did nothing to help her, prompting research into the bystander effect.