Friday the 13th: It’s not just a schlocky horror movie. Well, it is that, but depending on who you ask, it’s also a day to stay in bed with the covers pulled up over your head lest all kinds of misfortune and disaster befall you. There are two such days in 2013 -- in September and December – and they fall in what certain superstitious folks known as triskaidekaphobes consider the unluckiest year of the century. The poor humble number 13, feared and vilified for centuries. And for what? OK, so Apollo 13 is the only unsuccessful moon mission. And there were 13 people at the Last Supper, and a few other dinner parties that ended badly. Lots of serial killers have 13 letters in their name, it’s true. Oh yes, and good luck finding the 13th floor in most skyscrapers. Never mind that children officially become teenagers at age 13. Now that’s scary. Here are some other reasons the number 13 has gotten such a bad rap.