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评论
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2位数,f=1:20个素数p11<p<=97:13、17、19、23、29、31、37、41、43、47、53、59、61、67、71、73、79、83、89、97
2位数,f=2:没有素数,因为abab有除数101、abba和aabb除数11
2位数字,f=3:无素数作为数字之和3*(a+b)
2位数,f=4:(a,b)有18种可能性:
(1,0), (1,3), (1,4), (1,6), (1,7), (1,9), (2,3), (2,9), (3,4), (3,5), (3,7), (3,8), (4,7), (4,9), (5,9), (6,7), (7,9), (8,9)
每种可能性都会发生,2+9+3+5+13+11+2+6+3+10+2+2+5+2+6+4=90=2*3^2*5个素数
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例子
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根据18种可能的“配对”分类的完整列表:
10010101, 10011101
11313331, 11333131, 13111333, 13131133, 13131331, 13133311, 13311313, 31133131, 33113131
14441411, 41414411, 44114141
16166611, 16616161, 61116661, 61661161, 66161611
11171777, 11177717, 17111777, 17171177, 17171771, 17177117, 17711717, 17717171, 71117177, 71171717, 71717117, 77111717, 77711171
11919199, 11919991, 19111999, 19199119, 19911919, 19991911, 91919911, 91999111, 99111919, 99119191, 99919111
23223323, 32323223
22929299、29229929、29299229、29992229、92922299、99292229
34434343, 44334343, 44343433
35553533, 53355353, 53533553
33373777, 33773737, 37373773, 37377337, 73337377, 73337773, 73373737, 73773373, 77337373, 77733373
38383883, 88838333
47447747, 77474447
44994949, 49444999, 49494499, 49499449, 94449499
55599959, 99555959
67766767, 76767667
77997979, 79779979, 79797997, 79997977, 99977797, 99979777
88989899, 98988899, 98989889, 99898889
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