**13**is a prime number.

13 has a representation as a sum of two squares: 13 = 2

^{2}+ 3^{2}.

13 is the 7th Fibonacci number.

11 and 13 form a twin prime pair.

**is a13**

*lucky*number. To build the

*lucky*number sequence, start with natural numbers. Delete every second number, leaving 1, 3, 5, 7, 9, 11,

**13**, 15, 17, 19, 21, . . . . The second number remaining is 3, so delete every third number, leaving 1, 3, 7, 9,

**13**, 15, 19, 21, . . . .The next number remaining is 7, so delete every 7th number, leaving 1, 3, 7, 9,

**13**, 15, 21, . . . . The next number remaining is 9, so delete every ninth number, and so on. The numbers that remain are lucky: 3, 7, 9,

**13**, 15, 21, 25, . . . .

**13**

^{2}= 169 and (reversing all digits) 31

^{2}= 961.

Three planes can cut a doughnut into a maximum of

**13**parts.

**13**is 111 in base 3.

The fear of the number

**13**is called triskaidekaphobia.

There are

**13**tricks in each hand of bridge.

Source: Number Gossip; Prime Curios!