3311

Number
$3311$ (three thousand, three hundred and eleven) is:


 * $7 \times 11 \times 43$


 * The $21$st square pyramidal number after $1$, $5$, $14$, $30$, $55$, $\ldots$, $1015$, $1240$, $1496$, $1785$, $2109$, $2470$, $2870$:
 * $3311 = \displaystyle \sum_{k \mathop = 1}^{21} k^2 = \dfrac {21 \left({21 + 1}\right) \left({2 \times 21 + 1}\right)} 6$