# The Center of Math Blog

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## Friday, May 13, 2016

### Friday the 13th

Did you know today is Friday the 13th?

Spanning across many cultures and religions, the number 13 tends to have unlucky connotations. Furthermore, it may be a gateway to the weekend for some, but Friday also has historical and religious connections with 'evil' or 'unluckiness'. This being said, it is not surprising that the two culminate in what has been deemed the most unlucky day, Friday the 13th. This suspicion has been furthered by horror movies and pop culture. The legend and superstition began, and psychologists have tried to pinpoint why. Many say that because of the predisposed feelings towards Friday the 13th , people become more aware of unlucky or negative events. Whatever your feelings or superstitions, we have gathered 13 facts about the number 13. Hopefully with a few fun facts in your pocket, your Friday the 13th will be as lucky as any other day!

13 facts about the number 13!

1. Thirteen is often referred to as a baker's dozen.

2. (13)²= 169 and (31)²=961

3. 13 is the  6th  prime number

4. Triskaidekaphobia is the fear of the number 13. People who suffered from triskaidekaphobia include Winston Churchill (who refused to sit in row 13 of an aircraft or theatre), Napoleon, and Christopher Columbus.

5. 13 is the 7th   Fibonacci number.

 Tridecagon
6. (1/13)=0.076923076923076923076923...
(rational periodic infinite decimal)

7. A thirteen-sided polygon is called a tridecagon. The interior angle measure in a regular tridecagon is 152.3077 degrees.

8. 13 can also be called a Long Dozen.

9. 13 is the smallest emirp, a prime number whose digit reversal forms a different prime number (31 is prime). Other emirp pairs include 17 & 71, 79 & 97, and 1193 & 3911.

10. Many office buildings and hotels do not have a Floor 13. This is also true for some city streets.

12 . 13 holds a special significance for the United States.
There were 13 original colonies. There are 13 stripes on the American flag.

The US \$1.00 has:
13 levels of the pyramid
13 stars
13 arrows
13 stripes
13 leaves
13 olives

The Great Seal of the United States has:
13 stars
13 arrows
13 berries
13 stripes
13 leaves

13. If Friday the 13th is something you dread, in China and Italy, 13 is considered a lucky number! The same is true of Colgate University, in New York.