Fatto matematico: 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!).
Data storica: April 4th is the day in 1850 that the Great Fire of Cottenham, a large part of the Cambridgeshire village (England) is burnt to the ground under suspicious circumstances.