Fatto matematico: 7421 is a value of n for which 4n and 5n together use each digit exactly once.
Trivia: 7421 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Data storica: April 25th is the day in 1849 that the Governor General of Canada, Lord Elgin, signs the Rebellion Losses Bill, outraging Montreal's English population and triggering the Montreal Riots.