Fatto matematico: 2663 is the number of digits of the 20^{th} perfect number.
Trivia: 2663 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Data storica: April 16th is the day in 1521 that Martin Luther's first appearance before the Diet of Worms to be examined by the Holy Roman Emperor Charles V and the other estates of the empire.