A month has to start on a Sunday for the 13th to fall on a Friday.
There can be no more than three in the same calendar year.
All years will have at least one.
Fourteen months is the longest you can go without seeing one.
The fear of Friday the 13th is called Friggatriskaidekaphobia or paraskevidekatriaphobia.
Triskaidekaphobia, or the fear of the number 13, is even more widespread. So much so that many high-rise buildings, hotels, and hospitals skip the 13th floor and many airports do not have gates numbered 13. In many parts of the world, having 13 people at the dinner table is considered bad luck, according to Timeanddate.com.
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