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#8471f66f-507c-449a-8a70-ae695378c336基础解答题数列求和方法数列

21.(2023•黄冈模拟)设等差数列{an}\{a_{n}\}nn项和SnS_{n}a1=1a_{1}=1,满足2Sn+1=n(an+5)+22S_{n+1}=n(a_{n}+5)+2nNn\in N^{\cdot }
(1)求数列{an}\{a_{n}\}的通项公式;
(2)记bn=n+1SnSn+2{b}_{n}=\frac{n+1}{{S}_{n}{S}_{n+2}},设数列{bn}\{b_{n}\}的前nn项和为TnT_{n},求证Tn<516{T}_{n}<\frac{5}{16}