13 (thirteen) is the natural number following 12 and preceding 14.
Strikingly folkloric aspects of the number 13 have been noted in various cultures around the world: one theory is that this is due to the cultures employing lunar-solar calendars (there are approximately 12.41 lunations per solar year, and hence 12 "true months" plus a smaller, and often portentous, thirteenth month). This can be witnessed, for example, in the "Twelve Days of Christmas" of Western European tradition.
Movies:
13 (2006), 13 (2010), Thirteen (1974), Thirteen (2003), Thirteen (2016)