1240

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Number

$1240$ (one thousand, two hundred and forty) is:

$2^3 \times 5 \times 31$

The $15$th square pyramidal number after $1$, $5$, $14$, $30$, $55$, $91$, $140$, $204$, $285$, $385$, $506$, $650$, $819$, $1015$:

$1240 = \ds \sum_{k \mathop = 1}^{15} k^2 = \dfrac {15 \paren {15 + 1} \paren {2 \times 15 + 1} } 6$

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