8. From the vertices of a regular 1680-gon, several are chosen and connected in sequence to form polygons. The number of regular polygons that can be formed is

保留源文本的换行和格式，所以翻译结果如下：

8. From the vertices of a regular 1680-gon, several are chosen and connected in sequence to form polygons. The number of regular polygons that can be formed is
$1680=2^{4} \cdot 3 \cdot 5 \cdot 7$, the sum of its divisors is $\left(1+2+2^{2}+2^{3}+2^{4}\right)(1+3)(1+5)(1+7)=5952$, noting that 1680 and 840 do not meet the requirements, so the number of regular polygons is $5952-2520=3432$.