14 (number)

14 (fourteen) is the natural number following 13 and preceding 15.

Fourteen is the seventh composite number.

14 is the third distinct semiprime, being the third of the form ${\displaystyle 2\times q}$ (where ${\displaystyle q}$ is a higher prime). More specifically, it is the first member of the second cluster of two discrete semiprimes (14, 15); the next such cluster is (21, 22), members whose sum is the fourteenth prime number, 43.

14 has an aliquot sum of 10, within an aliquot sequence of two composite numbers (14, 10, 8, 7, 1, 0) in the prime 7-aliquot tree.

14 is the third companion Pell number and the fourth Catalan number. It is the lowest even ${\displaystyle n}$ for which the Euler totient ${\displaystyle \varphi (x)=n}$ has no solution, making it the first even nontotient.

According to the Shapiro inequality, 14 is the least number ${\displaystyle n}$ such that there exist ${\displaystyle x_{1}}$, ${\displaystyle x_{2}}$, ${\displaystyle x_{3}}$, where:

with ${\displaystyle x_{n+1}=x_{1}}$ and ${\displaystyle x_{n+2}=x_{2}.}$

A set of real numbers to which it is applied closure and complement operations in any possible sequence generates 14 distinct sets. This holds even if the reals are replaced by a more general topological space; see Kuratowski's closure-complement problem.