38

Number
$38$ (thirty-eight) is:


 * $2 \times 19$


 * The $14$th semiprime after $4, 6, 9, 10, 14, 15, 21, 22, 25, 26, 33, 34, 35$:
 * $38 = 2 \times 19$


 * The magic constant of the order 3 magic hexagon.


 * The $4$th nontotient after $14, 26, 34$:
 * $\nexists m \in \Z_{>0}: \phi \left({m}\right) = 38$
 * where $\phi \left({m}\right)$ denotes the Euler $\phi$ function


 * The $14$th Ulam number after $1, 2, 3, 4, 6, 8, 11, 13, 16, 18, 26, 28, 36$:
 * $36 = 2 + 36$

Also see

 * Magic Constant of Order 3 Magic Hexagon