A216837 - cp's OEIS frontend

A216837 Number of permutations p of {1,...,n} such that at most one element of {p(1),...,p(i-1)} is between p(i) and p(i+1) for all i from 1 to n-1.

n	a(n)
0	1
1	1
2	2
3	6
4	20
5	72
6	268
7	1020
8	3936
9	15332
10	60112
11	236780
12	935848
13	3708236
14	14721912
15	58533264
16	232991656
17	928261480
18	3700935760
19	14763921580
20	58924038816
21	235258847064
22	939576469152
23	3753419774180
24	14997257109992
25	59933657096280
26	239547378220840

[1, 1, 2, 6, 20, 72, 268, 1020, 3936, 15332, 60112, 236780, 935848, 3708236, 14721912, 58533264, 232991656, 928261480, 3700935760, 14763921580, 58924038816, 235258847064, 939576469152, 3753419774180, 14997257109992, 59933657096280, 239547378220840]

cp's OEIS Frontend

A216837 Number of permutations p of {1,...,n} such that at most one element of {p(1),...,p(i-1)} is between p(i) and p(i+1) for all i from 1 to n-1.

Table of values

List of values