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A240168
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T(n,k) is the number of unlabeled graphs of n vertices and k edges that have endpoints, where an endpoint is a vertex with degree 1.
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1
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0, 1, 1, 1, 1, 2, 2, 1, 1, 2, 3, 5, 4, 2, 1, 1, 2, 4, 8, 13, 15, 16, 11, 5, 2, 1, 1, 2, 4, 9, 19, 35, 55, 75, 83, 72, 51, 29, 13, 5, 2, 1, 1, 2, 4, 10, 22, 50, 105, 196, 338, 511, 649, 695, 627, 473, 304, 172, 83, 35, 14, 5, 2, 1
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OFFSET
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1,6
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COMMENTS
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The length of the rows are 1,1,2,4,7,11,16,22,...: (n-1)*(n-2)/2 + 1 = A152947(n).
T(n,k) = 0 if k > (n-1)*(n-2)/2 + 1. (Cf. A245796)
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LINKS
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EXAMPLE
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First few rows of irregular triangle are:
..0
..1
..1....1
..1....2....2....1
..1....2....3....5....4....2....1
..1....2....4....8...13...15...16...11....5....2....1
..1....2....4....9...19...35...55...75...83...72...51...29...13....5....2....1
...
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CROSSREFS
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KEYWORD
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nonn,tabf
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AUTHOR
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STATUS
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approved
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