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A323656
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Number of non-isomorphic multiset partitions of weight n with exactly 2 distinct vertices, or with exactly 2 (not necessarily distinct) edges.
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5
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0, 0, 2, 4, 14, 28, 69, 134, 285, 536, 1050, 1918, 3566, 6346, 11363, 19771, 34405, 58677, 99797, 167223, 279032, 460264, 755560, 1228849, 1988680, 3193513, 5103104, 8100712, 12798207, 20102883, 31434374, 48900337, 75746745, 116787611, 179342230, 274238159
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OFFSET
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0,3
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COMMENTS
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The weight of a multiset partition is the sum of sizes of its parts. Weight is generally not the same as number of vertices.
Also the number of nonnegative integer matrices with only two columns, no zero rows or columns, and sum of entries equal to n, up to row and column permutations.
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LINKS
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FORMULA
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EXAMPLE
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Non-isomorphic representatives of the a(2) = 2 through a(4) = 14 multiset partitions with exactly 2 distinct vertices:
{{12}} {{122}} {{1122}}
{{1}{2}} {{1}{22}} {{1222}}
{{2}{12}} {{1}{122}}
{{1}{2}{2}} {{11}{22}}
{{12}{12}}
{{1}{222}}
{{12}{22}}
{{2}{122}}
{{1}{1}{22}}
{{1}{2}{12}}
{{1}{2}{22}}
{{2}{2}{12}}
{{1}{1}{2}{2}}
{{1}{2}{2}{2}}
Non-isomorphic representatives of the a(2) = 2 through a(4) = 14 multiset partitions with exactly 2 edges:
{{1}{1}} {{1}{11}} {{1}{111}}
{{1}{2}} {{1}{22}} {{11}{11}}
{{1}{23}} {{1}{122}}
{{2}{12}} {{11}{22}}
{{12}{12}}
{{1}{222}}
{{12}{22}}
{{1}{233}}
{{12}{33}}
{{1}{234}}
{{12}{34}}
{{13}{23}}
{{2}{122}}
{{3}{123}}
Inequivalent representatives of the a(4) = 14 matrices:
[2 2] [1 3]
.
[1 0] [1 0] [0 1] [2 0] [1 1] [1 1]
[1 2] [0 3] [1 2] [0 2] [1 1] [0 2]
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[1 0] [1 0] [1 0] [0 1]
[1 0] [0 1] [0 1] [0 1]
[0 2] [1 1] [0 2] [1 1]
.
[1 0] [1 0]
[1 0] [0 1]
[0 1] [0 1]
[0 1] [0 1]
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PROG
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(PARI) EulerT(v)={Vec(exp(x*Ser(dirmul(v, vector(#v, n, 1/n))))-1, -#v)}
seq(n)={concat(0, (EulerT(vector(n, k, k+1)) + EulerT(vector(n, k, if(k%2, 0, (k+6)\4))))/2 - EulerT(vector(n, k, 1)))} \\ Andrew Howroyd, Aug 26 2019
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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