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A029889
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Number of graphical partitions (degree-vectors for graphs with n vertices, allowing self-loops which count as degree 1; or possible ordered row-sum vectors for a symmetric 0-1 matrix).
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17
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1, 2, 5, 14, 43, 140, 476, 1664, 5939, 21518, 78876, 291784, 1087441, 4077662, 15369327, 58184110, 221104527, 842990294, 3223339023
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OFFSET
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0,2
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COMMENTS
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I call loops of degree one half-loops, so these are half-loop-graphs or graphs with half-loops. - Gus Wiseman, Dec 31 2020
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REFERENCES
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R. A. Brualdi, H. J. Ryser, Combinatorial Matrix Theory, Cambridge Univ. Press, 1992.
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LINKS
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FORMULA
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Calculated using Cor. 6.3.3, Th. 6.3.6, Cor. 6.2.5 of Brualdi-Ryser.
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EXAMPLE
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The a(0) = 1 through a(3) = 14 sorted degree sequences:
() (0) (0,0) (0,0,0)
(1) (1,0) (1,0,0)
(1,1) (1,1,0)
(2,1) (2,1,0)
(2,2) (2,2,0)
(1,1,1)
(2,1,1)
(3,1,1)
(2,2,1)
(3,2,1)
(2,2,2)
(3,2,2)
(3,3,2)
(3,3,3)
For example, the half-loop-graph
{{1,3},{3}}
has degrees (1,0,2), so (2,1,0) is counted under a(3). The half-loop-graphs
{{1},{1,2},{1,3},{2,3}}
{{1},{2},{3},{1,2},{1,3}}
both have degrees (3,2,2), so (3,2,2) is counted under a(3).
(End)
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MATHEMATICA
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Table[Length[Union[Sort[Table[Count[Join@@#, i], {i, n}]]&/@Subsets[Subsets[Range[n], {1, 2}]]]], {n, 0, 5}] (* Gus Wiseman, Dec 31 2020 *)
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CROSSREFS
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Non-half-loop-graphical partitions are conjectured to be counted by A321728.
The covering case (no zeros) is A339843.
A004251 counts degree sequences of graphs, with covering case A095268.
A320663 counts unlabeled multiset partitions into singletons/pairs.
A339659 is a triangle counting graphical partitions.
A339844 counts degree sequences of loop-graphs, with covering case A339845.
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KEYWORD
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nonn,more
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AUTHOR
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torsten.sillke(AT)lhsystems.com
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EXTENSIONS
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STATUS
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approved
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