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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.

A144087 a(n) is the number of partial bijections (or subpermutations) of an n-element set with exactly 2 fixed points.

Table of values

n a(n)
0 0
1 0
2 1
3 3
4 24
5 180
6 1620
7 16380
8 184800
9 2298240
10 31222800
11 459874800
12 7296791040
13 124047443520
14 2248897210560
15 43301275617600
16 882304501478400
17 18964350332928000
18 428768570841811200
19 10170992126597702400
20 252555415474602240000
21 6550785133563775104000
22 177151172210521513804800

List of values

[0, 0, 1, 3, 24, 180, 1620, 16380, 184800, 2298240, 31222800, 459874800, 7296791040, 124047443520, 2248897210560, 43301275617600, 882304501478400, 18964350332928000, 428768570841811200, 10170992126597702400, 252555415474602240000, 6550785133563775104000, 177151172210521513804800]

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

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