A319252 - cp's OEIS frontend

A319252 Triangle read by rows: T(n,k) is the number of permutations pi of [n] with k+1 valleys such that s(pi) avoids the patterns 132, 231, 312, and 321, where s denotes West's stack-sorting map (0 <= k <= floor((n-1)/2)).

n	a(n)
1	1
2	2
3	4
4	2
5	8
6	10
7	16
8	36
9	4
10	32
11	112
12	36
13	64
14	320
15	200
16	10
17	128
18	864
19	880
20	130
21	256
22	2240
23	3360
24	980
25	28
26	512
27	5632
28	11648
29	5600
30	476
31	1024
32	13824
33	37632
34	26880
35	4536
36	84
37	2048
38	33280
39	115200
40	114240
41	31920
42	1764

[1, 2, 4, 2, 8, 10, 16, 36, 4, 32, 112, 36, 64, 320, 200, 10, 128, 864, 880, 130, 256, 2240, 3360, 980, 28, 512, 5632, 11648, 5600, 476, 1024, 13824, 37632, 26880, 4536, 84, 2048, 33280, 115200, 114240, 31920, 1764]

cp's OEIS Frontend

A319252 Triangle read by rows: T(n,k) is the number of permutations pi of [n] with k+1 valleys such that s(pi) avoids the patterns 132, 231, 312, and 321, where s denotes West's stack-sorting map (0 <= k <= floor((n-1)/2)).

Table of values

List of values