A319251 - cp's OEIS frontend

A319251 Triangle read by rows: T(n,k) is the number of permutations pi of [n] with k descents such that s(pi) avoids the patterns 132, 231, 312, and 321, where s denotes West's stack-sorting map.

n	a(n)
1	1
2	1
3	1
4	1
5	4
6	1
7	1
8	8
9	8
10	1
11	1
12	13
13	28
14	13
15	1
16	1
17	19
18	70
19	70
20	19
21	1
22	1
23	26
24	145
25	250
26	145
27	26
28	1
29	1
30	34
31	266
32	700
33	700
34	266
35	34
36	1
37	1
38	43
39	448
40	1666
41	2548
42	1666
43	448
44	43
45	1
46	1
47	53
48	708
49	3528
50	7644
51	7644
52	3528
53	708
54	53
55	1

[1, 1, 1, 1, 4, 1, 1, 8, 8, 1, 1, 13, 28, 13, 1, 1, 19, 70, 70, 19, 1, 1, 26, 145, 250, 145, 26, 1, 1, 34, 266, 700, 700, 266, 34, 1, 1, 43, 448, 1666, 2548, 1666, 448, 43, 1, 1, 53, 708, 3528, 7644, 7644, 3528, 708, 53, 1]

cp's OEIS Frontend

A319251 Triangle read by rows: T(n,k) is the number of permutations pi of [n] with k descents such that s(pi) avoids the patterns 132, 231, 312, and 321, where s denotes West's stack-sorting map.

Table of values

List of values