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 $1, 2, 3, 4, 6, 8, 11, 13, 16, 18, 26, 28, 36$:
 * $36 = 2 + 36$


 * The $14$th and largest even number after $2, 4, 6, 8, 10, 12, 14, 16, 20, 22, 26, 28, 32$ which cannot be expressed as the sum of $2$ composite odd numbers.


 * The common sum of the smallest triplet of consecutive positive even integers $n$ with the property $n + \tau \left({n}\right) = m$ for some $m$:
 * $38 = 30 + \tau \left({30}\right) = 32 + \tau \left({32}\right) = 34 + \tau \left({34}\right)$


 * The $5$th integer after $7, 13, 19, 35$ the decimal representation of whose square can be split into two parts which are each themselves square:
 * $38^2 = 1444; 144 = 12^2, 4 = 2^2$


 * The $24$th positive integer after $2, 3, 4, 7, 8, \ldots, 26, 29, 30, 31, 32, 33, 37$ which cannot be expressed as the sum of distinct pentagonal numbers.

Also see

 * Magic Constant of Order 3 Magic Hexagon
 * Smallest Consecutive Even Numbers such that Added to Divisor Count are Equal