287

Number
$287$ (two hundred and eighty-seven) is:


 * $7 \times 41$


 * The $14$th pentagonal number after $1$, $5$, $12$, $22$, $35$, $51$, $70$, $92$, $117$, $145$, $176$, $210$, $247$:
 * $287 = \displaystyle \sum_{k \mathop = 1}^{14} \left({3 k - 2}\right) = \dfrac {14 \left({3 \times 14 - 1}\right)} 2$


 * The $27$th generalized pentagonal number after $1$, $2$, $5$, $7$, $12$, $15$, $\ldots$, $126$, $145$, $176$, $187$, $210$, $222$, $247$, $260$:
 * $287 = \dfrac {14 \left({3 \times 14 - 1}\right)} 2$