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1²;+3²;+5²;+.+15²;=1²;+2²;+3²;+…+15²;-(2²;+4²;+…+14²;)=15*16*31/6-4*(1²;+2²;+…+7²;)=1240-4*7*8*15/6=1240-560=680或者1²;+3²;+5²…
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