4.
已知公比不为\(1\)的等比数列\(\{a_{n}\}\)的前\(3\)项积为\(27\),且\(2a_{2}\)为\(3a_{1}\)和\(a_{3}\)的等差中项.
\((1)\)求数列\(\{a_{n}\}\)的通项公式\(a_{n}\);
\((2)\)若数列\(\{b_{n}\}\)满足\(b_{n}=b_{n-1}⋅\log _{3}a_{n+1}(n\geqslant 2,n∈N^{*})\),且\(b_{1}=1\),求数列\(\{ \dfrac {b_{n}}{b_{n+2}}\}\)的前\(n\)项和\(S_{n}\).