406

Number
$406$ (four hundred and six) is:


 * $2 \times 7 \times 29$


 * The $28$th triangular number after $1$, $3$, $6$, $10$, $15$, $\ldots$, $171$, $190$, $210$, $231$, $253$, $276$, $300$, $325$, $351$, $378$:
 * $406 = \displaystyle \sum_{k \mathop = 1}^{28} k = \dfrac {28 \times \left({28 + 1}\right)} 2$


 * The $31$st untouchable number after $2$, $5$, $52$, $88$, $96$, $120$, $124$, $\ldots$, $324$, $326$, $336$, $342$, $372$