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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.

A132431 For n>0, let B_n be the subsemigroup of the full transformation monoid on the n-set [n] generated by the following functions: Let x be a certain element in [n]. Now the generators of B are those functions which map either x to any distinct element y in [n] leaving all the other elements fixed, or y to x leaving all the other elements fixed. Then a(n) = number of elements in B_n.

Table of values

n a(n)
1 0
2 2
3 9
4 88
5 1385
6 24336
7 466753
8 9906688
9 233522577
10 6093136000
11 174912502721
12 5487091383456
13 186891076515481
14 6870622015481056
15 271195480556337345
16 11440127985767481856
17 513639921634424850977
18 24455974520989478444544
19 1230835712617872016215265

List of values

[0, 2, 9, 88, 1385, 24336, 466753, 9906688, 233522577, 6093136000, 174912502721, 5487091383456, 186891076515481, 6870622015481056, 271195480556337345, 11440127985767481856, 513639921634424850977, 24455974520989478444544, 1230835712617872016215265]

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

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