在数列{an}中,a1=2,an+1=4an-3n+1,n∈N*.
(1)求证:数列{an-n}是等比数列;
(2)求数列{an}的前n项和Sn;
(3)求证:不等式Sn+1≤4Sn对任意n∈N*皆成立.
已知数列{an}的前n项和为Sn,3Sn=an-1(n∈N).
(1)求a1,a2;
(2)求证:数列{an}是等比数列;
(3)求an和Sn.
等比数列{an}的前n项和为Sn,已知S1,S3,S2成等差数列.
(1)求{an}的公比q;
(2)若a1-a3=3,求Sn.
等比数列{an}中,S3=7,S6=63,则an=________.
已知两个数k+9和6-k的等比中项是2k,则k=________.
等比数列{an}中,a1>0,a2a4+2a3a5+a4a6=36,则a3+a5=________.