Arnold Schoenberg was obsessed with numerology. He was the composer who developed the 12 tone system, a way of creating music wherein you don't re-use a pitch till all 12 have been played. He thought 12 was a perfect number, but 13 was bad luck so he tried his best to avoid the number all together. With Schoenberg, numbers were a powerful obsession, leading him even to avoiding writing bar 13 in his music, instead labeling it 12A. He even thought it had an effect on his health! He says this in a letter to a friend:
[Indeed, I am not so well at the moment. I am in my 65th year and you know that 5 times 13 is 65 and 13 is my bad number. But when this five-times-thirteen year has passed, then I have 13 more years.]
13 years later to the day he thought I know for sure I will die and sure enough, he died that night in his sleep on Friday, July 13, 1951. read more about him here: http://en.wikipedia.org/wiki/Arnold_Schoenberg