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A000080
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Number of nonisomorphic minimal triangle graphs.
(Formerly M1173 N0450)
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2
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1, 1, 2, 4, 9, 19, 48, 117, 307, 821, 2277, 6437, 18634, 54775, 163703, 495529, 1518706, 4703848, 14714754, 46444979, 147832051, 474229588, 1532565644
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OFFSET
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3,3
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COMMENTS
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Let T be a set of triples (sets of three distinct points) from a set of n points. The graph G(T) has a vertex for each point, with two vertices joined by an edge if the two points belong to one of the triples. Then a(n) is the number of ways to choose T so that G(T) is connected and minimal, meaning that it becomes disconnected if any triple is omitted. - N. J. A. Sloane, Jan 22 2014
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REFERENCES
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N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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EXAMPLE
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The triples on n = 3 through 6 points are (see "Illustration" link): 3 : ABC; 4 : ABC, ABD; 5 : ABC, ADE; and ABC, ABD, ABE, 6 : ABD, BCD, DEF; ABC, BCD, DEF; ABF, BCD, DEF; ABC, ABD, ABE, ABF. - N. J. A. Sloane, Jan 22 2014
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CROSSREFS
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KEYWORD
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nonn,more,nice
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AUTHOR
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EXTENSIONS
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Three more terms from Arlin Anderson (starship1(AT)gmail.com)
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STATUS
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approved
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