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数列{an}的前n项和为Sn,已知(n=1,2,…),则an=________
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数列{a
n}的前n项和为S
n,已知
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WmUyvTLsY5xmMo3B9ZVWmUyvDPsYp/8DWpgsfsz0+wIAAAAASUVORK5CYII=
)
(n=1,2,…),则a
n=________
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