14

Number
$14$ (fourteen) is:


 * $2 \times 7$


 * The $5$th semiprime after $4, 6, 9, 10$:
 * $14 = 2 \times 7$


 * The $3$rd square pyramidal number after $1, 5$:
 * $14 = 1 + 4 + 9$


 * The smallest natural number solution to $\sigma \left({n}\right) = \sigma \left({n + 1}\right)$


 * The smallest nontotient:
 * $\nexists m \in \Z_{>0}: \phi \left({m}\right) = 14$
 * where $\phi \left({m}\right)$ denotes the Euler $\phi$ function


 * The smallest Keith number:
 * $1, 4, 5, 9, 14, \ldots$

Also see

 * 12 times Sigma of 12 equals 14 times Sigma of 14