506

Number
$506$ (five hundred and six) is:


 * $2 \times 11 \times 23$


 * The $11$th square pyramidal number after $1$, $5$, $14$, $30$, $55$, $91$, $140$, $204$, $285$, $385$:
 * $506 = \displaystyle \sum_{k \mathop = 1}^{11} k^2 = \dfrac {11 \left({11 + 1}\right) \left({2 \times 11 + 1}\right)} 6$