408

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Number

$408$ (four hundred and eight) is:

$2^3 \times 3 \times 17$


The $12$th octagonal number, after $1$, $8$, $21$, $40$, $65$, $96$, $133$, $176$, $225$, $280$, $341$:
$408 = \ds \sum_{k \mathop = 1}^{12} \paren {6 k - 5} = 12 \paren {3 \times 12 - 2}$


The $32$nd untouchable number after $2$, $5$, $52$, $88$, $96$, $120$, $124$, $\ldots$, $324$, $326$, $336$, $342$, $372$, $406$


Also see