cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A190823 Number of permutations of 2 copies of 1..n introduced in order 1..n with no element equal to another within a distance of 2.

Table of values

n a(n)
0 1
1 0
2 0
3 1
4 10
5 99
6 1146
7 15422
8 237135
9 4106680
10 79154927
11 1681383864
12 39034539488
13 983466451011
14 26728184505750
15 779476074425297
16 24281301468714902
17 804688068731837874
18 28269541494090294129
19 1049450257149017422000
20 41050171013933837206545

List of values

[1, 0, 0, 1, 10, 99, 1146, 15422, 237135, 4106680, 79154927, 1681383864, 39034539488, 983466451011, 26728184505750, 779476074425297, 24281301468714902, 804688068731837874, 28269541494090294129, 1049450257149017422000, 41050171013933837206545]

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement.