A138552 - cp's OEIS frontend

A138552 Returning walks of length 2n on the upper half of the square lattice, distinct under reflections about the y-axis.

n	a(n)
0	1
1	2
2	11
3	90
4	889
5	9723
6	113322
7	1380522
8	17382365
9	224573349
10	2962117366
11	39741658047
12	540862505806
13	7450655906450
14	103713126384420
15	1456845308244810
16	20627719676855685
17	294136002612344145

[1, 2, 11, 90, 889, 9723, 113322, 1380522, 17382365, 224573349, 2962117366, 39741658047, 540862505806, 7450655906450, 103713126384420, 1456845308244810, 20627719676855685, 294136002612344145]

cp's OEIS Frontend

A138552 Returning walks of length 2n on the upper half of the square lattice, distinct under reflections about the y-axis.

Table of values

List of values