Fait mathématique: 1345 is the number of permutations of 8 elements that have 5^{th} power equal to the identity permutation.
Culture générale: 1345 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Date historique: September 6th is the day in 1991 that the name Saint Petersburg is restored to Russia's second largest city, which had been renamed Leningrad in 1924.