172

Number
$172$ (one hundred and seventy-two) is:


 * $2^2 \times 43$


 * The $2$nd of the $6$th pair of consecutive integers which both have $6$ divisors:
 * $\map {\sigma_0} {171} = \map {\sigma_0} {172} = 6$


 * The $16$th noncototient after $10$, $26$, $34$, $50$, $52$, $58$, $86$, $100$, $116$, $122$, $130$, $134$, $146$, $154$, $170$:
 * $\nexists m \in \Z_{>0}: m - \map \phi m = 172$
 * where $\map \phi m$ denotes the Euler $\phi$ function