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Search: id:A046858
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| A046858 |
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Irregular triangle read by rows: T(n,k) = number of directed graphs-with-loops with n nodes and k arcs (n >= 0, 0 <= k <= n(n+1)). |
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+0
2
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| 1, 1, 1, 1, 2, 4, 2, 1, 1, 2, 8, 17, 24, 24, 17, 8, 2, 1, 1, 2, 9, 32, 95, 203, 373, 515, 584, 515, 373, 203, 95, 32, 9, 2, 1, 1, 2, 9, 36, 157, 549, 1692, 4374, 9626, 17874, 28373, 38486, 44805, 44805, 38486, 28373, 17874, 9626, 4374, 1692, 549, 157, 36, 9, 2, 1, 1
(list; graph; listen)
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OFFSET
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0,5
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COMMENT
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Equivalently, T(n,k) = number of relations on n-set with strength k (n >= 0, 0<=k<=n^2).
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REFERENCES
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W. Oberschelp, Kombinatorische Anzahlbestimmungen in Relationen, Math. Ann., 174 (1967), 53-78.
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LINKS
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W. Oberschelp, Kombinatorische Anzahlbestimmungen in Relationen, Math. Ann., 174 (1967), 53-78.
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EXAMPLE
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Triangle begins:
[1],
[1, 1],
[1, 2, 4, 2, 1],
[1, 2, 8, 17, 24, 24, 17, 8, 2, 1],
[1, 2, 9, 32, 95, 203, 373, 515, 584, 515, 373, 203, 95, 32, 9, 2, 1] (the last batch giving the numbers of directed graphs with loops on 4 nodes and from 0 to 16 arcs).
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CROSSREFS
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Cf. A000595.
Adjacent sequences: A046855 A046856 A046857 this_sequence A046859 A046860 A046861
Sequence in context: A094239 A105023 A052285 this_sequence A132823 A059317 A087266
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KEYWORD
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nonn,tabf,nice
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AUTHOR
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njas
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EXTENSIONS
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More terms from Vladeta Jovovic (vladeta(AT)Eunet.yu), Feb 07 2000
Edited by njas Apr 16 2008 at the suggestion of Herman Jamke (hermanjamke(AT)fastmail.fm), Mar 24 2008
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