Samuel Clemens (Mark Twain) was born on and died on days when Halley’s Comet can be seen. During his life he predicted that he would die when it could be seen.
Triskaidekaphobia means fear of the number 13. Paraskevidekatriaphobia means fear of Friday the 13th (which occurs one to three times a year). In Italy, 17 is considered an unlucky number. In Japan, 4 is considered an unlucky number.