817

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Number

$817$ (eight hundred and seventeen) is:

$19 \times 43$

The $17$th centered hexagonal number after $1$, $7$, $19$, $37$, $61$, $91$, $127$, $169$, $217$, $271$, $331$, $397$, $469$, $547$, $631$, $721$:

$817 = \ds 1 + \sum_{k \mathop = 1}^{17 - 1} 6 k = 17^3 - 16^3$

Also see

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