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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.

A177797 Number of decomposable fixed-point free involutions, also the number of disconnected chord diagrams with 2n nodes on an open string.

Table of values

n a(n)
0 0
1 0
2 1
3 5
4 31
5 239
6 2233
7 24725
8 318631
9 4707359
10 78691633
11 1471482725
12 30469552111
13 692488851599
14 17141242421353
15 459033875802485
16 13221994489388791
17 407574126219013439
18 13386292717807416673
19 466636446695213384645
20 17205919477720642772671
21 669019022588385113932079
22 27357684052927560953626393

List of values

[0, 0, 1, 5, 31, 239, 2233, 24725, 318631, 4707359, 78691633, 1471482725, 30469552111, 692488851599, 17141242421353, 459033875802485, 13221994489388791, 407574126219013439, 13386292717807416673, 466636446695213384645, 17205919477720642772671, 669019022588385113932079, 27357684052927560953626393]

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

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