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The Da Vinci Code popularized a lot of rather sketchy theories, among them that superstitions about Friday the 13th go back to the day the Knights Templar were wiped out by royal order in 1307. Although there's no real agreement among experts, one far more likely idea is that it hearkens back to the Christian banishment of the Norse goddess Friga (from whom the word Friday comes) and her re-imagination as a witch.
There's no doubt though that the number 13 holds more phobic cache than any other number in North American culture. No other, not even the vaunted number of coincidence 23, requires that it be stricken completely from apartment floor designation, on paper if not in fact.
Other cultures don't share the superstition. In China, 13 is considered a lucky number, while 4 is not. And even some segments of North American society celebrate instead of fear Friday the 13th. For example, bikers from all over the continent converge every Friday the 13th on the little tourist town of Port Dover Ontario on Lake Erie.
This year, that's a lot of biking; 2009 is one of the rare years that features three Friday the 13ths, in February, March, and November.
In English at least, fear of the number 13 is so widespread, or at least accepted as common, that it's got its own pathological term coined for it: triskaidekaphobia. An irrational love of the number 13 would conversely be triskaidekaphilia.
Not quite a million-dollar word, but worth a hell of a lot more than 13 points in Scrabble at least!