Fatto generale: 5531 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 5531 is an uninteresting number.
Trivia: 5531 is an unremarkable number.
Data storica: February 21st is the day in 1995 that Steve Fossett lands in Leader, Saskatchewan, Canada becoming the first person to make a solo flight across the Pacific Ocean in a balloon.