A274969 - cp's OEIS frontend

A274969 Number of walks in the first quadrant starting and ending at (0,0) consisting of 3n steps taken from {E=(1, 0), D=(-1, 1), S=(0, -1)}, no S step occurring before the final E step.

n	a(n)
0	1
1	1
2	4
3	21
4	121
5	728
6	4488
7	28101
8	177859
9	1134705
10	7283640
11	46981740
12	304253964
13	1976886616
14	12880883408
15	84130964709
16	550649378199
17	3610705776755
18	23714554702020
19	155979407872365
20	1027269675638745
21	6773476758296220
22	44709685668953760
23	295402076512228140
24	1953492865541875476

[1, 1, 4, 21, 121, 728, 4488, 28101, 177859, 1134705, 7283640, 46981740, 304253964, 1976886616, 12880883408, 84130964709, 550649378199, 3610705776755, 23714554702020, 155979407872365, 1027269675638745, 6773476758296220, 44709685668953760, 295402076512228140, 1953492865541875476]

cp's OEIS Frontend

A274969 Number of walks in the first quadrant starting and ending at (0,0) consisting of 3n steps taken from {E=(1, 0), D=(-1, 1), S=(0, -1)}, no S step occurring before the final E step.

Table of values

List of values