1785

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Number

$1785$ (one thousand, seven hundred and eighty-five) is:

$3 \times 5 \times 7 \times 17$

The $17$th square pyramidal number after $1$, $5$, $14$, $30$, $55$, $91$, $140$, $204$, $285$, $385$, $506$, $650$, $819$, $1015$, $1240$, $1496$:

$1785 = \ds \sum_{k \mathop = 1}^{17} k^2 = \dfrac {17 \paren {17 + 1} \paren {2 \times 17 + 1} } 6$

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