A135401 - cp's OEIS frontend

A135401 a(n) = number of permutations (p(1),p(2),p(3),...,p(n)) of (1,2,3,...n) each of which is its own inverse and is such that p(k) = n + 1 - p(n+1-k) for all k in the range 1 <= k <= n.

n	a(n)
0	1
1	1
2	2
3	2
4	6
5	6
6	20
7	20
8	76
9	76
10	312
11	312
12	1384
13	1384
14	6512
15	6512
16	32400
17	32400
18	168992
19	168992
20	921184
21	921184
22	5222208
23	5222208
24	30710464
25	30710464
26	186753920
27	186753920
28	1171979904
29	1171979904
30	7573069568
31	7573069568
32	50305536256
33	50305536256
34	342949298688

[1, 1, 2, 2, 6, 6, 20, 20, 76, 76, 312, 312, 1384, 1384, 6512, 6512, 32400, 32400, 168992, 168992, 921184, 921184, 5222208, 5222208, 30710464, 30710464, 186753920, 186753920, 1171979904, 1171979904, 7573069568, 7573069568, 50305536256, 50305536256, 342949298688]

cp's OEIS Frontend

A135401 a(n) = number of permutations (p(1),p(2),p(3),...,p(n)) of (1,2,3,...n) each of which is its own inverse and is such that p(k) = n + 1 - p(n+1-k) for all k in the range 1 <= k <= n.

Table of values

List of values