Mathematical fact: 5241 is the starting location of 7777 in the decimal expansion of p.
Trivia: 5241 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Historical date: May 7th is the day in 1429 that Joan of Arc ends the Siege of Orléans, pulling an arrow from her own shoulder and returning, wounded, to lead the final charge.