A297708 - cp's OEIS frontend

A297708 Number of permutations p of [n] such that p(p(i)) = i for all i or p(n+1-p(i)) = n+1-i for all i.

n	a(n)
0	1
1	1
2	2
3	6
4	14
5	46
6	132
7	444
8	1452
9	5164
10	18680
11	71080
12	278920
13	1135624
14	4774448
15	20692560
16	92381072
17	423566224
18	1994458656
19	9619233888
20	47516407008
21	239904464608
22	1237764055616
23	6515682543040
24	34984350444736
25	191360856810688
26	1065970229647232
27	6041353305197184

[1, 1, 2, 6, 14, 46, 132, 444, 1452, 5164, 18680, 71080, 278920, 1135624, 4774448, 20692560, 92381072, 423566224, 1994458656, 9619233888, 47516407008, 239904464608, 1237764055616, 6515682543040, 34984350444736, 191360856810688, 1065970229647232, 6041353305197184]

cp's OEIS Frontend

A297708 Number of permutations p of [n] such that p(p(i)) = i for all i or p(n+1-p(i)) = n+1-i for all i.

Table of values

List of values