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