General fact: 40 is the percentage of U.S. paper currency in circulation that was counterfeit by the end of the Civil War.
Mathematical fact: 40 is a repdigit in base 3 (1111) and a Harshad number in base 10.
Trivia: 40 is the number of years of marriage as the ruby wedding anniversary.
Historical date: February 9th is the day in 1996 that the Provisional Irish Republican Army declares the end to its 18 month ceasefire and explodes a large bomb in London's Canary Wharf.