726

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


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


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