172

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


 * $2^2 \times 43$


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


 * The $2$nd of the $6$th pair of consecutive integers which both have $6$ divisors:
 * $\tau \left({171}\right) = \tau \left({172}\right) = 6$