697

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


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