13 is a prime number.
13 has a representation as a sum of two squares: 13 = 22 + 32.
13 is the 7th Fibonacci number.
11 and 13 form a twin prime pair.
132 = 169 and (reversing all digits) 312 = 961.
Three planes can cut a doughnut into a maximum of 13 parts.
13 is 111 in base 3.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhebFXqrNmWmtULb_WXXa3OeoXhBNW-biVWYkPAacc7mBobhbXi5LDwHWTeRuU0D5qHTQ7ZMjhV5gOChaap25_Rb4PRXEgACrvE3cYDvtxEw60x0IBM-dMPSsbML-htnAS_QOcgpTJSLDI/s200/n0013.jpg)
The fear of the number 13 is called triskaidekaphobia.
There are 13 tricks in each hand of bridge.
Source: Number Gossip; Prime Curios!
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhebFXqrNmWmtULb_WXXa3OeoXhBNW-biVWYkPAacc7mBobhbXi5LDwHWTeRuU0D5qHTQ7ZMjhV5gOChaap25_Rb4PRXEgACrvE3cYDvtxEw60x0IBM-dMPSsbML-htnAS_QOcgpTJSLDI/s200/n0013.jpg)
The fear of the number 13 is called triskaidekaphobia.
There are 13 tricks in each hand of bridge.
Source: Number Gossip; Prime Curios!