4720

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Number

$4720$ (four thousand, seven hundred and twenty) is:

$2^4 \times 5 \times 59$

The $40$th octagonal number, after $1$, $8$, $21$, $40$, $65$, $\ldots$, $3008$, $3201$, $3400$, $3605$, $3816$, $4033$, $4256$, $4485$:

$4720 = \ds \sum_{k \mathop = 1}^{40} \paren {6 k - 5} = 40 \paren {3 \times 40 - 2}$

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