A185030 - cp's OEIS frontend

A185030 Number of permutations p of {1,...,n} such that exactly one element of {p(1),...,p(i-1)} is between p(i) and p(i+1) for all i from 2 to n-1.

n	a(n)
0	1
1	1
2	2
3	2
4	2
5	4
6	6
7	10
8	20
9	36
10	66
11	132
12	250
13	478
14	956
15	1854
16	3612
17	7224
18	14178
19	27898
20	55796
21	110246
22	218166
23	436332
24	865618
25	1718902
26	3437804
27	6837398
28	13607250
29	27214500
30	54216128
31	108053078
32	216106156
33	431001044
34	859831354
35	1719662708
36	3432314834

[1, 1, 2, 2, 2, 4, 6, 10, 20, 36, 66, 132, 250, 478, 956, 1854, 3612, 7224, 14178, 27898, 55796, 110246, 218166, 436332, 865618, 1718902, 3437804, 6837398, 13607250, 27214500, 54216128, 108053078, 216106156, 431001044, 859831354, 1719662708, 3432314834]

cp's OEIS Frontend

A185030 Number of permutations p of {1,...,n} such that exactly one element of {p(1),...,p(i-1)} is between p(i) and p(i+1) for all i from 2 to n-1.

Table of values

List of values