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(45) 思路:從1開始,每隔一個排列就是1、7、13、19、…… 也就是1+6=7,7+6=13,13+6=19,19+6=27、…… 再從9開始,每隔一個排列是9、27、45、63、…… 也就是1*9=9,3*9=27,5*9=45,7*9=63,9*9=81、……
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