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2n=130时,用错位两筛法求得,
(130-2)/2(1-2/3)(1-2/5)(1-2/7)(1-2/11)
=64(1/3)(3/5)(5/7)(9/11)=7.4805194805.
实际有:(13,19),(29,31),(41.43),(59.61),(71,73),(101,103),(107,109)。吻合
被筛掉的有(3,5),(5,7),(11,13),
和为128的素数对:
用简单比例两筛法
128/2(1-1/2)(1-2/3)(1-2/5)(1-2/11)=64(1/2)(1/3)(3/5)(5/7)(9/11)=3.7402597403
实际有:(19+109),(31+97), (1+127)不是,但站位.
被筛掉没有 |
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