Fatto generale: 1605 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 1605 is the number of 7-octs.
Trivia: 1605 is a boring number.
Data storica: May 23rd is the day in 1949 that the Federal Republic of Germany is established and the Basic Law for the Federal Republic of Germany is proclaimed.