优优班--学霸训练营 > 题目详情
  • 设数列\(\{a_{n}\}\)满足:\(①a_{1}=1\);\(②\)所有项\(a_{n}∈N^{*}\);\(③1=a_{1} < a_{2} < … < a_{n} < a_{n+1} < …\)设集合\(A_{m}=\{n|a_{n}\leqslant m,m∈N^{*}\}\),将集合\(A_{m}\)中的元素的最大值记为\(b_{m}.\)换句话说,\(b_{m}\)是数列\(\{a_{n}\}\)中满足不等式\(a_{n}\leqslant m\)的所有项的项数的最大值\(.\)我们称数列\(\{b_{n}\}\)为数列\(\{a_{n}\}\)的伴随数列\(.\)例如,数列\(1\),\(3\),\(5\)的伴随数列为\(1\),\(1\),\(2\),\(2\),\(3\).
    \((1)\)请写出数列\(1\),\(4\),\(7\)的伴随数列;
    \((2)\)设\(a_{n}=3^{n-1}\),求数列\(\{a_{n}\}\)的伴随数列\(\{b_{n}\}\)的前\(20\)之和;
    \((3)\)若数列\(\{a_{n}\}\)的前\(n\)项和\(S_{n}=n^{2}+c(\)其中\(c\)为常数\()\),求数列\(\{a_{n}\}\)的伴随数列\(\{b_{m}\}\)的前\(m\)项和\(T_{m}\).
    【考点】数列求和方法,等差数列与等比数列的综合应用
    【分析】请登陆后查看
    【解答】请登陆后查看
    难度:中等
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