9730

Number
$9730$ (nine thousand, seven hundred and thirty) is:


 * $2 \times 5 \times 7 \times 139$


 * The $139$th triangular number after $1$, $3$, $6$, $10$, $15$, $\ldots$, $8911$, $9045$, $9180$, $9316$, $9453$, $9591$:
 * $9730 = \displaystyle \sum_{k \mathop = 1}^{139} k = \dfrac {139 \times \left({139 + 1}\right)} 2$


 * The $70$th hexagonal number after $1$, $6$, $15$, $28$, $45$, $66$, $91$, $\ldots$, $8128$, $8385$, $8646$, $8911$, $9180$, $9453$:
 * $9730 = \displaystyle \sum_{k \mathop = 1}^{70} \left({4 k - 3}\right) = 70 \left({2 \times 70 - 1}\right)$