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.
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.
Terms
- a(0) =1a(1) =1a(2) =3a(3) =8a(4) =21a(5) =56a(6) =153a(7) =428a(8) =1222a(9) =3549a(10) =10454a(11) =31159a(12) =93801a(13) =284788a(14) =871007a(15) =2681018a(16) =8298932a(17) =25817395a(18) =80674901a(19) =253106836a(20) =796968055a(21) =2517706036a(22) =7977573202a(23) =25347126629a(24) =80738862084a(25) =257778971503a(26) =824798533932
External references
- oeis: A008909