715

Number
$715$ (seven hundred and fifteen) is:


 * $5 \times 11 \times 13$


 * The $22$nd pentagonal number after $1$, $5$, $12$, $22$, $35$, $51$, $70$, $92$, $117$, $145$, $176$, $210$, $247$, $287$, $330$, $330$, $376$, $425$, $477$, $532$, $590$, $651$:
 * $715 = \displaystyle \sum_{k \mathop = 1}^{22} \left({3 k - 2}\right) = \dfrac {22 \left({3 \times 22 - 1}\right)} 2$