The status of the number 13 in the United States is interesting. It is thought to be unlucky, but the power of the superstition is weak. You can see it most obviously in tall buildings. Most skyscrapers do not have a "thirteenth floor," or more precisely, no floor that is numbered 13. In an elevator, the numbers go directly from 12 to 14. Everybody says "Of course I don't believe in that silly superstition--but other people do." Building owners will say "it's harder to rent space on a floor that's numbered 13." I think this custom is fading and that newer buildings do have a "thirteenth floor."

There is a weak superstition that Fridays are unlucky, and, therefore, a feeling that any "Friday the 13th" is especially unlucky. Again, nobody takes it very seriously. Nevertheless, whenever the 13th of a month falls on a Friday, it is something that people are likely to mention in conversation. "Be careful today, it's Friday the Thirteenth!"

On the other hand, the United States was originally formed from thirteen colonies, forming a strip on the East Coast: New Hampshire, Vermont, Massachusetts, Connecticut, Rhode Island, New Jersey, Pennsylvania, Delaware, Maryland, Virginia, North Carolina, South Carolina, and Georgia). As a result, many U.S. national symbols are based on the number thirteen. The most obvious one is our flag, which has thirteen stripes. The Great Seal of the United States shows an eagle holding thirteen arrows, a shield with thirteen stripes, some kind of pattern containing thirteen stars, and on and on and on. 

Since nobody has mentioned it yet, I have to mention the word triskaidekaphobia, fear of the number thirteen. It is a silly word. Nobody ever really uses it. It just gets mentioned because people think it is cool that there is a name for it.