A155518 - cp's OEIS frontend

A155518 Number of permutations p of {1,2,...,n} such that p(j) + p(n+1-j) != n+1 for all j.

n	a(n)
0	1
1	0
2	0
3	4
4	16
5	64
6	384
7	2880
8	23040
9	208896
10	2088960
11	23193600
12	278323200
13	3640688640
14	50969640960
15	768126320640
16	12290021130240
17	209688566169600
18	3774394191052800
19	71921062285148160
20	1438421245702963200

[1, 0, 0, 4, 16, 64, 384, 2880, 23040, 208896, 2088960, 23193600, 278323200, 3640688640, 50969640960, 768126320640, 12290021130240, 209688566169600, 3774394191052800, 71921062285148160, 1438421245702963200]

cp's OEIS Frontend

A155518 Number of permutations p of {1,2,...,n} such that p(j) + p(n+1-j) != n+1 for all j.

Table of values

List of values