问题标题：
1.1,5,13,25...n2.3,9,18,30.n
问题描述：
1.1,5,13,25...n
2.3,9,18,30.n
陈印淇回答：
1、an=2n^2-2n
2、an=(3n^2+3n-6)/2n=2
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1.1,5,13,25...n
2.3,9,18,30.n