2.
已知数列\(\{a_{n}\}\)中\(a_{1}=1\),前\(n\)项和为\(S_{n}\),若对任意的\(n∈N*\),均有\(S_{n}=a_{n+k}-k(k\)是常数,且\(k∈N*)\)成立,则称数列\(\{a_{n}\}\)为“\(H(k)\)数列”.
\((1)\)若数列\(\{a_{n}\}\)为“\(H(1)\)数列”,求数列\(\{a_{n}\}\)的前\(n\)项和\(S_{n}\);
\((2)\)若数列\(\{a_{n}\}\)为“\(H(2)\)数列”,且\(a_{2}\)为整数,试问:是否存在数列\(\{a_{n}\}\),使得\(|a \;_{ n }^{ 2 }-a_{n-1}a_{n+1}|\leqslant 40\)对一切\(n\geqslant 2\),\(n∈N*\)恒成立?如果存在,求出这样数列\(\{a_{n}\}\)的\(a_{2}\)的所有可能值,如果不存在,请说明理由;
\((3)\)若数列\(\{a_{n}\}\)为“\(H(k)\)数列”,且\(a_{1}=a_{2}=…=a_{k}=1\),证明:\(a_{n+2k}\geqslant (1+ \dfrac {1}{2^{k-1}})^{n-k}\).