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例子
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三角形开始:
1
0 1
0 1 1
0 0 3 1
0 0 3 6 1
0 0 0 15 10 1
0 0 15 45 15 1
0 0 0 0 105 105 21 1
0 0 0 0 105 420 210 28 1
0 0 0 0 0 945 1260 378 36 1
如上所述,a(n)是{1..n}到k个单体或对的集合分区数。这也是{1..n}的子集到n-k对中的集合分区数。在第一种情况下,行n=5统计以下集合分区:
{{1},{2,3},{4,5}} {{1},{2},{3},{4,5}} {{1},{2},{3},{4},{5}}
{{1,2},{3},{4,5}} {{1},{2},{3,4},{5}}
{{1,2},{3,4},{5}} {{1},{2,3},{4},{5}}
{{1,2},{3,5},{4}} {{1,2},{3},{4},{5}}
{{1},{2,4},{3,5}} {{1},{2},{3,5},{4}}
{{1},{2,5},{3,4}} {{1},{2,4},{3},{5}}
{{1,3},{2},{4,5}}{1},{2,5},{3},{4}}
{{1,3},{2,4},{5}} {{1,3},{2},{4},{5}}
{{1,3},{2,5},{4}} {{1,4},{2},{3},{5}}
{{1,4},{2},{3,5}} {{1,5},{2},{3},{4}}
{{1,4},{2,3},{5}}
{{1,4},{2,5},{3}}
{{1,5},{2},{3,4}}
{{1,5},{2,3},{4}}
{{1,5},{2,4},{3}}
在第二种情况下,我们有:
{{1,2},{3,4}} {{1,2}} {}
{{1,2},{3,5}} {{1,3}}
{{1,2},{4,5}}{1,4}}}
{{1,3},{2,4}} {{1,5}}
{{1,3},{2,5}} {{2,3}}
{{1,3},{4,5}} {{2,4}}
{{1,4},{2,3}} {{2,5}}
{{1,4},{2,5}} {{3,4}}
{{1,4},{3,5}} {{3,5}}
{{1,5},{2,3}} {{4,5}}
{{1,5},{2,4}}
{{1,5},{3,4}}
{{2,3},{4,5}}
{{2,4},{3,5}}
{{2,5},{3,4}}
(结束)
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