Fatto matematico: 509 is the index of a prime Fibonacci number.
Trivia: 509 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Data storica: May 23rd is the day in 1967 that Egypt closes the Straits of Tiran and blockades the port of Eilat at the northern end of the Gulf of Aqaba to Israeli shipping.