2870

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Number

$2870$ (two thousand, eight hundred and seventy) is:

$2 \times 5 \times 7 \times 41$

The $20$th square pyramidal number after $1$, $5$, $14$, $30$, $55$, $\ldots$, $1015$, $1240$, $1496$, $1785$, $2109$, $2470$:

$2870 = \ds \sum_{k \mathop = 1}^{20} k^2 = \dfrac {20 \paren {20 + 1} \paren {2 \times 20 + 1} } 6$

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