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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.

A309618 a(n) = Sum_{k=0..floor(n/2)} k! * 2^k * (n - 2*k)!.

Table of values

n a(n)
0 1
1 1
2 4
3 8
4 36
5 140
6 832
7 5376
8 42432
9 374592
10 3720960
11 40694784
12 486679296
13 6310114560
14 88168366080
15 1320468480000
16 21101183631360
17 358354687426560
18 6444941507297280
19 122367252835860480
20 2445878526994022400
21 51337143210820239360
22 1128918790687649955840

List of values

[1, 1, 4, 8, 36, 140, 832, 5376, 42432, 374592, 3720960, 40694784, 486679296, 6310114560, 88168366080, 1320468480000, 21101183631360, 358354687426560, 6444941507297280, 122367252835860480, 2445878526994022400, 51337143210820239360, 1128918790687649955840]

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

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