A008909 - cp's OEIS frontend

A008909 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 a path.

n	a(n)
1	1
2	1
3	3
4	8
5	21
6	56
7	153
8	428
9	1222
10	3549
11	10454
12	31159
13	93801
14	284788
15	871007
16	2681018
17	8298932
18	25817395
19	80674901
20	253106836
21	796968055
22	2517706036
23	7977573202
24	25347126629
25	80738862084
26	257778971503
27	824798533932
28	2644335308021
29	8493626448823

[1, 1, 3, 8, 21, 56, 153, 428, 1222, 3549, 10454, 31159, 93801, 284788, 871007, 2681018, 8298932, 25817395, 80674901, 253106836, 796968055, 2517706036, 7977573202, 25347126629, 80738862084, 257778971503, 824798533932, 2644335308021, 8493626448823]

cp's OEIS Frontend

A008909 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 a path.

Table of values

List of values