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 $2, 5, 52, 88, 96, 120, 124, \ldots, 324, 326, 336, 342, 372$.