课时知能训练
一、选择题
1.数列{an}中,an+1=a2n2an-5,已知该数列既是等差数列又是等比数列,则该数列的前20项的和等于( )
A.100 B.0或100
C.100或-100 D.0或-100
2.数列{an}的通项公式an=1n+n+2(n∈N*),若前n项和为Sn,则Sn为( )
A.n+2-1
B.n+2+n+1-2-1
C.12(n+2-1)
D.12(n+2+n+1-2-1)
3.(2012•惠州模拟)已知Sn为等差数列{an}的前n项和,若a1=-2010,S2 0102 010-S2 0042004=6,则S2011=( )
A.2011 B.2010 C.0 D.2
4.已知数列{an}:12,13+23,14+24+34,…,110+210+310+…+910,…,那么数列{bn}={1anan+1}的前n项和Sn为( )