General fact: 473 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Mathematical fact: 473 is the largest known number whose square and 4^{th} power use different digits.
Trivia: 473 is a boring number.
Historical date: April 17th is the day in 1984 that Police Constable Yvonne Fletcher is killed by gunfire from the Libyan People's Bureau in London during a small demonstration outside the embassy.