Hecho matemático: 639 is a number n whose 5^{th} root has a decimal part that begins with the digits of n.
Trivia: 639 is an unremarkable number.
Fecha histórica: September 30th is the day in 1791 that the National Constituent Assembly in Paris is dissolved; Parisians hail Maximilien Robespierre and Jérôme Pétion as "incorruptible patriots".