Tổng S=1/2017(2.3.C 2017 2+3.3^2.C 2017 3+4.3^3.C 2017 4

Câu hỏi :

Tổng $$\begin{gathered} S=\frac{1}{2017}(2.3C_{2017}^2+3.3^2{C}_{2017}^3 \\ +4.3^3{C}_{2017}^4+...+k.3^{k-1}{C}_{2017}^k \\ +...+2017.3^{2016}{C}_{2017}^{2017}) \end{gathered}$$ bằng