58

Number
$58$ (fifty-eight) is:
 * $2 \times 29$


 * The $21$st semiprime after $4$, $6$, $9$, $10$, $14$, $15$, $21$, $22$, $25$, $26$, $33$, $34$, $35$, $38$, $39$, $46$, $49$, $51$, $55$, $58$:
 * $58 = 2 \times 29$


 * The $6$th noncototient after $10$, $26$, $34$, $50$, $52$:
 * $\nexists m \in \Z_{>0}: m - \phi \left({m}\right) = 58$
 * where $\phi \left({m}\right)$ denotes the Euler $\phi$ function


 * The $5$th positive integer which cannot be expressed as the sum of a square and a prime:
 * $1$, $10$, $25$, $34$, $58$, $\ldots$


 * The $3$rd non-square positive integer which cannot be expressed as the sum of a square and a prime:
 * $10$, $34$, $58$, $\ldots$


 * The $4$th Smith number after $4$, $22$, $27$:
 * $5 + 8 = 2 + 2 + 9 = 13$