Fait mathématique: 8420 is the number of symmetric ways to fold a strip of 20 stamps.
Culture générale: 8420 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Date historique: January 19th is the day in 1997 that Yasser Arafat returns to Hebron after more than 30 years and joins celebrations over the handover of the last Israeli-controlled West Bank city.