A245377 - cp's OEIS frontend

A245377 Number of 2-alternating permutations of 1,2,...,n, that is, a(n) is the number of down/up permutations (A000111) of 1,2,...,n such that any two consecutive terms differ by at least two.

n	a(n)
0	1
1	1
2	0
3	0
4	1
5	4
6	17
7	80
8	422
9	2480
10	16095
11	114432
12	884969
13	7398464
14	66502048
15	639653632
16	6556170841
17	71340409600
18	821408397105
19	9977630263296
20	127518757153174
21	1710576547456000
22	24030971882538671
23	352843606806499328

[1, 1, 0, 0, 1, 4, 17, 80, 422, 2480, 16095, 114432, 884969, 7398464, 66502048, 639653632, 6556170841, 71340409600, 821408397105, 9977630263296, 127518757153174, 1710576547456000, 24030971882538671, 352843606806499328]

cp's OEIS Frontend

A245377 Number of 2-alternating permutations of 1,2,...,n, that is, a(n) is the number of down/up permutations (A000111) of 1,2,...,n such that any two consecutive terms differ by at least two.

Table of values

List of values