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0 = 1*1 - 1 3 = 2*2 - 1 8 = 3*3 - 1 15 = 4*4 - 1 24 = 5*5 - 1 則它的2005個數= 2005*2005 - 1 = 4020024 第N個數是= N^2 - 1 (^2表示平方)
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