Fatto matematico: 4550 is the Stirling number of the second kind S(15,13).
Trivia: 4550 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Data storica: June 15th is the day in 1985 that Rembrandt's painting Danaë is attacked by a man (later judged insane) who throws sulfuric acid on the canvas and cuts it twice with a knife.