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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.

A024420 a(n) = n! * Sum_{j=0..floor(n/2)} (-1)^j/binomial(n,j).

Table of values

n a(n)
0 1
1 1
2 1
3 4
4 22
5 108
6 612
7 4416
8 36576
9 331200
10 3319200
11 36806400
12 445046400
13 5813579520
14 81716947200
15 1230656716800
16 19761225523200
17 336973967769600
18 6082189179494400
19 115851849523200000
20 2322322137354240000
21 48869666136023040000

List of values

[1, 1, 1, 4, 22, 108, 612, 4416, 36576, 331200, 3319200, 36806400, 445046400, 5813579520, 81716947200, 1230656716800, 19761225523200, 336973967769600, 6082189179494400, 115851849523200000, 2322322137354240000, 48869666136023040000]

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

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