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A097392
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The number of hierarchies with at least one subhierarchy composed of exactly 3 levels and no subhierarchy with more than 3 levels.
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1
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OFFSET
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1,4
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LINKS
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EXAMPLE
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Let : denote the separation between two subhierarchies, e.g. 2:3 are two subhierarchies where subhierarchy s=1 contains two elements and subhierarchy s=2 contains three elements. Let | denote the separation between two levels, e.g. 2|2|1 is a hierarchy composed of three levels with two elements on levels l=1 and l=2 and one element on level l=3. For n=5 one has a(5) = 12 hierarchies where at least one subhierarchy has exactly 3 levels (and no level l > 3 is allowed):
3|1|1; 1|3|1; 1|1|3; 2|2|1; 2|1|2; 1|2|2; 1|1|1:2; 1|1|1:1:1; 1|1|1:1|1;
2|1|1:1; 1|2|1:1; 1|1|2:1.
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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