8385

Number
$8385$ (eight thousand, three hundred and eighty-five) is:


 * $3 \times 5 \times 13 \times 43$


 * The $129$th triangular number after $1$, $3$, $6$, $10$, $15$, $\ldots$, $7503$, $7626$, $7750$, $7875$, $8001$, $8128$, $8256$:
 * $8385 = \displaystyle \sum_{k \mathop = 1}^{129} k = \dfrac {129 \times \left({129 + 1}\right)} 2$


 * The $65$th hexagonal number after $1$, $6$, $15$, $28$, $45$, $66$, $91$, $\ldots$, $6903$, $7140$, $7381$, $7626$, $7875$, $8128$:
 * $8385 = \displaystyle \sum_{k \mathop = 1}^{65} \left({4 k - 3}\right) = 65 \left({2 \times 65 - 1}\right)$