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, 1, 2, 9, 26, 122, 466, 2299, 10316, 54179

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