Fait mathématique: 2391 is the number of ways to flip a coin 12 times and get at least 3 heads in a row.
Culture générale: 2391 is a boring number.
Date historique: July 18th is the day in 1914 that the U.S. Congress forms the Aviation Section, U.S. Signal Corps, giving definite status to aircraft within the U.S. Army for the first time.