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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.

A308726 The number of permutations of length n and tier at most 1, that is, the number of permutations of length n sortable by two passes through a stack where outputting the longest prefix matching the identity permutation is prioritized.

Table of values

n a(n)
0 1
1 1
2 2
3 6
4 24
5 112
6 556
7 2811
8 14234
9 71808
10 360568
11 1803100
12 8988924
13 44719588
14 222221416
15 1103827306
16 5484124128
17 27265300504
18 135695994964
19 676228846370
20 3374996253420
21 16871826671280
22 84488005896720
23 423828619074900
24 2129868537725916
25 10722045181336524

List of values

[1, 1, 2, 6, 24, 112, 556, 2811, 14234, 71808, 360568, 1803100, 8988924, 44719588, 222221416, 1103827306, 5484124128, 27265300504, 135695994964, 676228846370, 3374996253420, 16871826671280, 84488005896720, 423828619074900, 2129868537725916, 10722045181336524]

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

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