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(2009北京西城高三抽样测试,理18)已知数列{an}的前n项和为Sn,a1=1,数列{an+Sn}是公差为2的等差数列.
(1)求a2,a3;
(2)证明数列{an-2}为等比数列;
(3)求数列{nan}的前n项和Tn.