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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.

A145220 a(n) is the number of even permutations (of an n-set) with exactly 2 fixed points.

Table of values

n a(n)
2 1
3 0
4 0
5 20
6 45
7 504
8 3640
9 33480
10 333585
11 3671360
12 44053416
13 572698620
14 8017774765
15 120266629560
16 1924266062160
17 32712523070864
18 588825415257345
19 11187682889912640
20 223753657798223920
21 4698826813762738020
22 103374189902780192781
23 2377606367763944486840

List of values

[1, 0, 0, 20, 45, 504, 3640, 33480, 333585, 3671360, 44053416, 572698620, 8017774765, 120266629560, 1924266062160, 32712523070864, 588825415257345, 11187682889912640, 223753657798223920, 4698826813762738020, 103374189902780192781, 2377606367763944486840]

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

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