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Search: id:A137813
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| A137813 |
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Minimal number of points needed to make a topology having k open sets. |
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+0
2
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| 0, 1, 2, 2, 3, 3, 4, 3, 4, 4, 5, 4, 5, 5, 5, 4, 5, 5, 6, 5, 6, 6, 6, 5, 6, 6, 6, 6, 7, 6, 7, 5, 6, 6, 7, 6, 7, 7, 7, 6, 7, 7, 7, 7, 7, 7, 8, 6, 7, 7, 7, 7, 8, 7, 8, 7, 8, 8, 8, 7, 8, 8, 8, 6, 7, 7, 8, 7, 8, 8, 8, 7, 8, 8, 8, 8, 8, 8, 9, 7, 8, 8, 8, 8, 8, 8, 9, 8, 9, 8, 9, 8, 9, 9, 9, 7, 8, 8, 8, 8, 9, 8, 9, 8, 9
(list; graph; listen)
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OFFSET
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1,3
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REFERENCES
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K. Ragnarsson and B. E. Tenner, Obtainable sizes of topologies on finite sets, preprint.
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EXAMPLE
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A topology having 7 open sets can be made on 4 points. The open sets are: {}, {1}, {2}, {1,2}, {1,3}, {1,2,3}, {1,2,3,4}. No topology having 7 open sets can be made with fewer points.
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CROSSREFS
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Cf. A137814.
Sequence in context: A139141 A122953 A128998 this_sequence A003313 A117497 A117498
Adjacent sequences: A137810 A137811 A137812 this_sequence A137814 A137815 A137816
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KEYWORD
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nonn
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AUTHOR
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Bridget Eileen Tenner (bridget(AT)math.depaul.edu), Feb 11 2008
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