1045

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Number

$1045$ (one thousand, one hundred and forty-five) is:

$5 \times 11 \times 19$

The $19$th octagonal number, after $1$, $8$, $21$, $40$, $65$, $96$, $133$, $176$, $225$, $280$, $341$, $408$, $481$, $560$, $645$, $736$, $833$, $936$:

$1045 = \ds \sum_{k \mathop = 1}^{19} \paren {6 k - 5} = 19 \paren {3 \times 19 - 2}$

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