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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.

A255515 1/n! times the number of ordered pairs of permutation functions f,g on n elements where f(f(x)) = g(f(g(x))).

Table of values

n a(n)
0 1
1 1
2 1
3 2
4 4
5 5
6 9
7 17
8 26
9 46
10 87
11 137
12 246
13 474
14 791
15 1420
16 2783
17 4839
18 8806
19 17361
20 31252
21 57613
22 114497
23 211496
24 395637
25 791597
26 1495016
27 2834242
28 5710510
29 10986325
30 21101677
31 42796060
32 83674582
33 162695172
34 332141014
35 658589710
36 1295551257
37 2661881254

List of values

[1, 1, 1, 2, 4, 5, 9, 17, 26, 46, 87, 137, 246, 474, 791, 1420, 2783, 4839, 8806, 17361, 31252, 57613, 114497, 211496, 395637, 791597, 1495016, 2834242, 5710510, 10986325, 21101677, 42796060, 83674582, 162695172, 332141014, 658589710, 1295551257, 2661881254]

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

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