3.
\((\)选作\()\)设数列\(\{a_{n}\}\)的前\(n\)项和为\(S_{n}\),\(a_{1}=1\),满足\( \overrightarrow{a}=(S_{n+1}-2S_{n},S_{n})\),\( \overrightarrow{b}=(2,n)\),\( \overrightarrow{a}/\!/ \overrightarrow{b}\).
\((1)\)求证:数列\(\{ \dfrac {S_{n}}{n}\}\)为等比数列;
\((2)\)求数列\(\{S_{n}\}\)的前\(n\)项和\(T_{n}\).