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A049463
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Number of basic interval orders of length n.
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0
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1, 2, 7, 34, 219, 1787, 17936, 216169, 3069552, 50562672, 953877927, 20389082457, 489301660818, 13080166471127, 386841424466953, 12581201258360820, 447574544428423114, 17333939484785264282, 727718718839603466267
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OFFSET
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2,2
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COMMENTS
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One may represent a basic length n interval order using n distinct endpoints. The removal of any element from such an order yields an interval order with shorter length.
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REFERENCES
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Amy N. Myers, Results in Enumeration and Topolgoy of Interval Orders, Ph.D. Thesis at Dartmouth College.
Amy N. Myers, Basic Interval Orders, Order, Volume: 16, Issue: 3, 1999, pp. 261-275.
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LINKS
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Table of n, a(n) for n=2..20.
More information
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FORMULA
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A recurrence in three variables exists.
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EXAMPLE
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a(2)=1 since {[ 1,1 ],[ 2,2 ]} is the unique basic interval order with two distinct endpoints.
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CROSSREFS
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Sequence in context: A185324 A135882 A143740 * A029894 A110313 A000944
Adjacent sequences: A049460 A049461 A049462 * A049464 A049465 A049466
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KEYWORD
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nonn,nice,easy
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AUTHOR
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Amy N. Myers (Amy.Myers(AT)Alum.Dartmouth.ORG)
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STATUS
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approved
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