如图,已知点\(D\)为\(\triangle ABC\)的边\(BC\)上一点,\( \overrightarrow{BD}=3 \overrightarrow{DC}\),\(E_{n}(n∈N_{+})\)为边\(AC\)上的一列点,满足\( \overrightarrow{E_{n}A}= \dfrac {1}{4}a_{n+1} \overrightarrow{E_{n}B}-(3a_{n}+2) \overrightarrow{E_{n}D}\),其中实数列\(\{a_{n}\}\)中
\(a_{n} > 0\),\(a_{1}=1\),则\(\{a_{n}\}\)的通项公式为\((\) \()\)