5720

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Number

$5720$ (five thousand, seven hundred and twenty) is:

$2^3 \times 5 \times 11 \times 13$


The $44$th octagonal number, after $1$, $8$, $21$, $40$, $65$, $\ldots$, $3816$, $4033$, $4256$, $4485$, $4720$, $4961$, $5208$, $5461$:
$5720 = \ds \sum_{k \mathop = 1}^{44} \paren {6 k - 5} = 44 \paren {3 \times 44 - 2}$


Also see