Cho f(n)=(n^2+n+1)^2 mọi n thuộc N*. Đặt

Câu hỏi :

Cho $f\left(n\right)={(n^2+n+1)}^2$ ∀n∈N* Đặt $u_n=\frac{f\left(1\right).f\left(3\right)...f(2n-1)}{f\left(2\right).f\left(4\right)...f\left(2n\right)}$.