对于数列
,若存在正整数
,使得对任意正整数
,都有
(其中
为非零常数),则称数列
是以
为周期,以
为周期公比的“类周期性等比数列”.若“类周期性等比数列”的前4项为1,1,2,3,周期为4,周期公比为3,则数列
前21项的和为__ .
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21-22高二下·上海长宁·期中 查看更多[3]
上海市延安中学2021-2022学年高二下学期期中数学试题(已下线)专题11 数列前n项和的求法 微点7 并项法求和(已下线)期中模拟预测卷02(测试范围:选修一全部内容)-【满分全攻略】2022-2023学年高二数学下学期核心考点+重难点讲练与测试(沪教版2020选修一+选修二)
更新时间:2023-02-28 23:46:35
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【推荐1】在数列的每相邻两项之间插入此两项的积,形成新的数列,这样的操作叫做该数列的一次"扩展".将数列1,2进行"扩展",第一次得到数列1,2,2;第二次得到数列1,2,2,4,2;....扩展得到的数列的第6项为___________ ;设第n次“扩展"后得到的数列为
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【推荐2】已知数列{an}的通项公式为an=
·3n-1,n∈N*,[an]表示不超过an的最大整数(如[1.2]=1).记bn=[an],数列{bn}的前n项和为Tn,若不等式λan+1>Tn+5n-
对任意的n∈N*恒成立,则实数λ的取值范围是________ .
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【推荐1】取出数列
的任意连续四项,若其中奇数项之和,偶数项之和均为同一个常数
(如连续四项
,
,
,
,满足
),则称数列
为错位等和数列,其中常数
是公和.若
表示
的前
项和,有如下命题:
(1)若一个等差数列是错位等和数列,则
;
(2)若一个等比数列是错位等和数列,则
;
(3)若
,则错位等和数列一定是最小正周期为4的周期数列;
(4)在错位等和数列
中,
,且
,若
是偶数,则
;
其中,真命题的序号是________
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(1)若一个等差数列是错位等和数列,则
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(2)若一个等比数列是错位等和数列,则
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(3)若
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(4)在错位等和数列
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其中,真命题的序号是
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【推荐2】若数列
满足
,则称数列
为“差递减”数列.若数列
是“差递减”数列,且其通项
与其前
项和
满足
,则实数
的取值范围是_________ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
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