A155519 - cp's OEIS frontend

A155519 a(n) = Sum (J(p): p is a permutation of {1,2,...,n}), where J(p) is the number of j <= ceiling(n/2) such that p(j) + p(n+1-j) = n+1.

n	a(n)
1	1
2	2
3	4
4	16
5	72
6	432
7	2880
8	23040
9	201600
10	2016000
11	21772800
12	261273600
13	3353011200
14	46942156800
15	697426329600
16	11158821273600
17	188305108992000
18	3389491961856000
19	64023737057280000
20	1280474741145600000

[1, 2, 4, 16, 72, 432, 2880, 23040, 201600, 2016000, 21772800, 261273600, 3353011200, 46942156800, 697426329600, 11158821273600, 188305108992000, 3389491961856000, 64023737057280000, 1280474741145600000]

cp's OEIS Frontend

A155519 a(n) = Sum (J(p): p is a permutation of {1,2,...,n}), where J(p) is the number of j <= ceiling(n/2) such that p(j) + p(n+1-j) = n+1.

Table of values

List of values