5.
若正项数列\(\{a_{n}\}\)的前\(n\)项和为\(S_{n}\),首项\(a_{1}=1\),\(P\left( \sqrt{{{S}_{n}}},{{S}_{n+1}} \right)\)点在曲线\(y=(x+1)^{2}\)上\(.\)
\((1)\)求数列\(\{a_{n}\}\)的通项公式\(a_{n}\);
\((2)\)设\({{b}_{n}}=\dfrac{1}{{{a}_{v}}\cdot {{a}_{n+1}}}\),\(T_{n}\)表示数列\(\{b_{n}\}\)的\(n\)项和,若\(T_{n}\geqslant a\)恒成立,求\(T_{n}\)及实数\(a\)的取值范围.