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A008910 Join 2n points on a line with n arcs above the line; form graph with the arcs as nodes, joining 2 nodes when the arcs cross. a(n) is the number of cases in which the graph is symmetric about middle and has no isolated nodes. 0
0, 1, 2, 9, 26, 122, 466, 2299, 10316, 54179 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Table of n, a(n) for n=1..10.

CROSSREFS

Sequence in context: A125670 A222660 A182325 * A239059 A153977 A051746

Adjacent sequences:  A008907 A008908 A008909 * A008911 A008912 A008913

KEYWORD

nonn

AUTHOR

klazar(AT)kam.mff.cuni.cz (Martin Klazar)

STATUS

approved

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Last modified August 14 18:13 EDT 2022. Contains 356122 sequences. (Running on oeis4.)