540

Number
$540$ (five hundred and forty) is:
 * $2^2 \times 3^3 \times 5$


 * The $15$th heptagonal number after $1, 7, 18, 34, 55, 81, 112, 148, 189, 235, 286, 342, 403, 469$:
 * $540 = \displaystyle \sum_{k \mathop = 1}^{15} \left({5 k - 4}\right) = \dfrac {15 \left({5 \times 15 - 3}\right)} 2$


 * The $43$rd untouchable number after $2, 5, 52, 88, 96, 120, 124, \ldots, 406, 408, 426, 430, 448, 472, 474, 498, 516, 518, 520, 530$.