Fatto generale: 531 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 531 is the smallest number with the property that its first 4 multiples contain the digit 1.
Trivia: 531 is an uninteresting number.
Data storica: June 14th is the day in 1962 that the European Space Research Organisation is established in Paris – later becoming the European Space Agency.