3400

Number
$3400$ (three thousand, four hundred) is:


 * $2^3 \times 5^2 \times 17$


 * The $34$th octagonal number, after $1$, $8$, $21$, $40$, $65$, $\ldots$, $2296$, $2465$, $2640$, $2821$, $3008$, $3201$:
 * $3400 = \displaystyle \sum_{k \mathop = 1}^{34} \left({6 k - 5}\right) = 34 \left({3 \times 34 - 2}\right)$