设数列9,99,999,9999,…的前n项和为______.
设数列9,99,999,9999,…的前n项和为______.
设数列{an}的前n项和Sn=n2,则a8=______.
设Sn是等差数列{an}的前n项和,若a4=9,S3=15,则数列{an}的通项为______.
设等差数列{an}满足a3=5,a10=-9,Sn是数列{an}的前n项和,则Sn的最大值为______.
设数列{an}前n项和为Sn,数列{Sn}的前n项和为Tn,满足Tn=2Sn-n2,n∈N*.
设a为常数,求数列a,2a2,3a2,…,nan的前n项和.
设数列前n项和为Sn.
设数列{an}的前n项和为Sn=2an-2n,
设数列{an}的前n项和为Sn,点(n,S
设数列{an}的前n项和为Sn,且Sn=2^n-1.
设数列{an}的前n项和为Sn,a1=10,a(n+1)=9Sn+10
设数列{an}的前n项和为Sn,且对任意正整数n,an+Sn=4096.