13 (thirteen) is a positive integer following 12 and preceding 14. Its ordinal form is written "13th" or "thirteenth".

Properties Edit

13 is an odd prime number.

13 is the smallest emirp in base 10.

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

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.

Ironically, it is the 5th lucky number (in the mathematical sense).

In googologyEdit

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

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