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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.

A002807 a(n) = Sum_{k=3..n} (k-1)!*C(n,k)/2.

Table of values

n a(n)
0 0
1 0
2 0
3 1
4 7
5 37
6 197
7 1172
8 8018
9 62814
10 556014
11 5488059
12 59740609
13 710771275
14 9174170011
15 127661752406
16 1904975488436
17 30341995265036
18 513771331467372
19 9215499383109573
20 174548332364311563
21 3481204991988351553
22 72920994844093191553
23 1600596371590399671784

List of values

[0, 0, 0, 1, 7, 37, 197, 1172, 8018, 62814, 556014, 5488059, 59740609, 710771275, 9174170011, 127661752406, 1904975488436, 30341995265036, 513771331467372, 9215499383109573, 174548332364311563, 3481204991988351553, 72920994844093191553, 1600596371590399671784]

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

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