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【简答题】
已知公差不为0的等差数列{a n }的首项a 1 （a 1 ∈R），且 1 a 1 ， 1 a 2 ， 1 a 4 成等比数列． （Ⅰ）求数列{a n }的通项公式； （Ⅱ）对n∈N * ，试比较 1 a 2 + 1 a 2 2 + 1 a 2 3 +…+ 1 a 2 n 与 1 a1 的大小．
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