506

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Number

$506$ (five hundred and six) is:

$2 \times 11 \times 23$

The $11$th square pyramidal number after $1$, $5$, $14$, $30$, $55$, $91$, $140$, $204$, $285$, $385$:

$506 = \ds \sum_{k \mathop = 1}^{11} k^2 = \dfrac {11 \paren {11 + 1} \paren {2 \times 11 + 1} } 6$

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