172

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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

Also see

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