Mathematical fact: 825 is the number of ways to legally add 2 sets of parentheses to a product of 9 variables.
Trivia: 825 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Historical date: April 4th is the day in 1841 that William Henry Harrison dies of pneumonia becoming the first President of the United States to die in office and the one with the shortest term served.