1140

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Number

$1140$ (one thousand, one hundred and forty) is:

$2^2 \times 3 \times 5 \times 19$

The $18$th tetrahedral number, after $1$, $4$, $10$, $20$, $35$, $56$, $84$, $120$, $165$, $220$, $286$, $364$, $455$, $560$, $680$, $816$, $969$:

$1140 = \ds \sum_{k \mathop = 1}^{18} \frac {k \paren {k + 1} } 2 = \dfrac {18 \paren {18 + 1} \paren {18 + 2} } 6$

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