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A057271
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Triangle T(n,k) of number of digraphs with a source and a sink on n labeled nodes and k arcs, k=0,1,..,n*(n-1).
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2
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1, 0, 2, 1, 0, 0, 6, 20, 15, 6, 1, 0, 0, 0, 24, 234, 672, 908, 792, 495, 220, 66, 12, 1, 0, 0, 0, 0, 120, 2544, 16880, 55000, 111225, 161660, 183006, 167660, 125945, 77520, 38760, 15504, 4845, 1140, 190, 20, 1
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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REFERENCES
| V. Jovovic, G. Kilibarda, Enumeration of labeled initially-finally connected digraphs, Scientific review, Serbian Scientific Society, 19-20 (1996), p. 245.
V. Jovovic, G. Kilibarda, Enumeration of labeled quasi-initially connected digraphs, Discrete Math., 224 (2000),151-163.
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EXAMPLE
| [1],[0,2,1],[0,0,6,20,15,6,1],[0,0,0,24,234,672,908,792,495,220,66,12,1],...; Number of digraphs with a source and a sink on 3 labeled nodes is 48=6+20+15+6+1.
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CROSSREFS
| Row sums give A049524. Cf. A057270, A057272-A057279.
Sequence in context: A185663 A105868 A057275 * A021480 A201299 A057274
Adjacent sequences: A057268 A057269 A057270 * A057272 A057273 A057274
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KEYWORD
| nonn,tabf
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AUTHOR
| Vladeta Jovovic, Goran Kilibarda (vladeta(AT)eunet.rs), Sep 14 2000
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