A007999 - cp's OEIS frontend

A007999 a(n) is the number of permutations w of 1,2,...,n such that both w and w^{-1} are alternating.

n	a(n)
0	1
1	1
2	1
3	1
4	2
5	3
6	8
7	19
8	64
9	213
10	880
11	3717
12	18288
13	92935
14	531440
15	3147495
16	20525168
17	138638825
18	1015694832
19	7700244745
20	62623847536
21	526317901451
22	4705365925872
23	43407723925499
24	423149546210416
25	4250149857500861
26	44868038386273776
27	487341646372204813

[1, 1, 1, 1, 2, 3, 8, 19, 64, 213, 880, 3717, 18288, 92935, 531440, 3147495, 20525168, 138638825, 1015694832, 7700244745, 62623847536, 526317901451, 4705365925872, 43407723925499, 423149546210416, 4250149857500861, 44868038386273776, 487341646372204813]

cp's OEIS Frontend

A007999 a(n) is the number of permutations w of 1,2,...,n such that both w and w^{-1} are alternating.

Table of values

List of values