697

Number
$697$ (six hundred and ninety-seven) is:
 * $17 \times 41$


 * The $17$th heptagonal number after $1, 7, 18, 34, 55, 81, 112, 148, 189, 235, 286, 342, 403, 469, 540, 616$:
 * $697 = \displaystyle \sum_{k \mathop = 1}^{17} \left({5 k - 4}\right) = \dfrac {17 \left({5 \times 17 - 3}\right)} 2$