Thirteen (13) is a positive integer one more than 12 and one less than 14.

## PropertiesEdit

13 is the sixth prime number (between 11 and 17). It is a member of a twin prime pair with 11.

13 is a Mersenne prime exponent, producing 8191.

13 is the seventh Fibonacci number, between 8 and 21.

13 is the fourth busy beaver number \(\Sigma(4) = 13\), the largest known value of the function. \(\Sigma(5)\) is known to be at least \(4098\).

13 is associated with bad luck in Western superstition.

A set of 13 objects is sometimes called a **baker's dozen**.

## In googology Edit

In Greek-based number-naming systems, 13 is associated with prefix "**trideka-**", and with prefix "**tredec-**" in Latin systems.

Sbiis Saibian calls the number **triaxis**, and it's equal to 10+3 using the addition.

Despite widely being considered unlucky, it is a lucky number (between 9 and 15).

13 is the current lower bound for the mathematical problem where Graham's number arose.