Fatto generale: 13403 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 13403 is an uninteresting number.
Trivia: 13403 is an uninteresting number.
Data storica: September 10th is the day in 1976 that a British Airways Hawker Siddeley Trident and an Inex-Adria DC-9 collide near Zagreb, Yugoslavia, killing 176.