1x2x3+2x4x6+4x8x12+7x14x21/1x3x5+2x6x10+4x12x20+7x21x35怎么做?
1x2x3+2x4x6+4x8x12+7x14x21
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1x3x5+2x6x10+4x12x20+7x21x35