数列{an}中,a1=1,an-an+1=2an•an+1,n∈N*,求an. |
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数列{an}中,a1=3,an-an+1=5an•an+1,n∈N*,求an. |
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已知数列{an}前n项和为Sn,求下列条件下数列的通项公式an. (1); (2)a1=2,an+1=an+3n+2; (3)a1=1,; (4)a1=1,an+1=3an+2. |
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求下列数列的前n项和Sn: (1)a,2a2,3a3,…,nan,…; (2)1×3,2×4,3×5,4×6,… |
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已知等比数列{an}中,a1=3,a4=81,若数列{bn}满足bn=log3an,则数列{}的前n项和Sn=______. |
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数列1•n,2(n-1),3(n-2),…,n•1的和为( ) A.n(n+1)(n+2) B.n(n+1)(2n+1) C.n(n+2)(n+3) D.n(n+1)(n+2) |
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数列{an}的通项公式为an=(-1)n-1•(4n-3),则它的前100项之和S100等于( ) A.200 B.-200 C.400 D.-400 |
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若数列an的通项公式为an=2n+2n-1,则数列an的前n项和为( ) A.2n+n2-2 B.2n+1+n2-1 C.2n+1+n2-2 D.2n+n-2 |
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在等比数列{an}(n∈N*)中,若,则该数列的前10项和为( ) A. B. C. D. |
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在等比数列{an}中,若公比q=4,前3项的和等于21,则该数列的通项公式an= . | |