4.
设\(S_{n}\)为正项数列\(\{a_{n}\}\)的前\(n\)项和,满足\(2S_{n}=a \;_{ n }^{ 2 }+a_{n}-2\).
\((I)\)求\(\{a_{n}\}\)的通项公式;
\((II)\)若不等式\((1+ \dfrac {2}{a_{n}+t})\;^{a_{n}}\geqslant 4\)对任意正整数\(n\)都成立,求实数\(t\)的取值范围;
\((III)\)设\(b_{n}=e\;^{ \frac {3}{4}a_{n}\ln (n+1)}(\)其中\(r\)是自然对数的底数\()\),求证:\( \dfrac {b_{1}}{b_{3}}+ \dfrac {b_{2}}{b_{4}}+..+ \dfrac {b_{n}}{b_{n+2}} < \dfrac { \sqrt {6}}{6}\).