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A063687
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Number of 2-trees rooted at any symmetric edge.
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2
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1, 1, 1, 2, 3, 6, 10, 21, 38, 84, 156, 352, 677, 1562, 3054, 7148, 14196, 33603, 67474, 161121, 326519, 785305, 1603111, 3878194, 7965845, 19365811, 39983300, 97610247, 202424674, 495955345, 1032460679, 2537529717, 5300256499
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listen;
history;
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OFFSET
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0,4
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REFERENCES
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F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 75, Eq. (3.5.9).
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LINKS
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Table of n, a(n) for n=0..32.
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CROSSREFS
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Cf. A058870, A058866, A054581.
Sequence in context: A008928 A124343 A032291 * A002988 A138347 A211180
Adjacent sequences: A063684 A063685 A063686 * A063688 A063689 A063690
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KEYWORD
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nonn,changed
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AUTHOR
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Vladeta Jovovic, Aug 22 2001
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STATUS
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approved
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