1247

Number
$1247$ (one thousand, two hundred and forty-seven) is:


 * $29 \times 43$


 * The $29$th pentagonal number after $1$, $5$, $12$, $22$, $35$, $\ldots$, $477$, $532$, $590$, $651$, $715$, $782$, $852$, $925$, $1001$, $1080$, $1162$:
 * $1247 = \displaystyle \sum_{k \mathop = 1}^{29} \left({3 k - 2}\right) = \dfrac {29 \left({3 \times 29 - 1}\right)} 2$