726

Number
$726$ (seven hundred and twenty-six) is:


 * $2 \times 3 \times 11^2$


 * The $11$th pentagonal pyramidal number after $1, 6, 12, 40, 75, 126, 196, 288, 405, 550$:
 * $726 = \displaystyle \sum_{k \mathop = 1}^{11} \dfrac {k \left({3 k - 1}\right)} 2 = \dfrac {11^2 \left({11 + 1}\right)} 2$