已知数列\(\{a _{n} \}\)的相邻两项\(a _{n}\)，\(a _{n+1}\)是关于\(x\)的方程\(x^{2}-2^{n}x+b_{n}=0(n∈N^{*})\)的两实根，且\(a _{1} =1\)．
\((\)Ⅰ\()\)求\(a _{2}\)，\(a _{3}\)，\(a _{4}\)的值；
\((\)Ⅱ\()\)求证：数列\(\{a_{n}- \dfrac {1}{3}×2^{n}\}\)是等比数列，并求数列\(\{a _{n} \}\)的通项公式．