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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.

A307354 a(n) = Sum_{0<=i<=j<=n} (-1)^(i+j) * (i+j)!/(i!*j!).

Table of values

n a(n)
0 1
1 2
2 6
3 19
4 65
5 231
6 841
7 3110
8 11628
9 43834
10 166298
11 634140
12 2428336
13 9331688
14 35967462
15 138987715
16 538287881
17 2088842463
18 8119916647
19 31613327405
20 123251518641
21 481125828853
22 1880262896537
23 7355767408395
24 28803717914791
25 112887697489907
26 442784607413427

List of values

[1, 2, 6, 19, 65, 231, 841, 3110, 11628, 43834, 166298, 634140, 2428336, 9331688, 35967462, 138987715, 538287881, 2088842463, 8119916647, 31613327405, 123251518641, 481125828853, 1880262896537, 7355767408395, 28803717914791, 112887697489907, 442784607413427]

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

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