A135404 - cp's OEIS frontend

A135404 Gessel sequence: the number of paths of length 2m in the plane, starting and ending at (0,1), with unit steps in the four directions (north, east, south, west) and staying in the region y > 0, x > -y.

n	a(n)
0	1
1	2
2	11
3	85
4	782
5	8004
6	88044
7	1020162
8	12294260
9	152787976
10	1946310467
11	25302036071
12	334560525538
13	4488007049900
14	60955295750460
15	836838395382645
16	11597595644244186
17	162074575606984788
18	2281839419729917410
19	32340239369121304038
20	461109219391987625316
21	6610306991283738684600

[1, 2, 11, 85, 782, 8004, 88044, 1020162, 12294260, 152787976, 1946310467, 25302036071, 334560525538, 4488007049900, 60955295750460, 836838395382645, 11597595644244186, 162074575606984788, 2281839419729917410, 32340239369121304038, 461109219391987625316, 6610306991283738684600]

cp's OEIS Frontend

A135404 Gessel sequence: the number of paths of length 2m in the plane, starting and ending at (0,1), with unit steps in the four directions (north, east, south, west) and staying in the region y > 0, x > -y.

Table of values

List of values