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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.

A005161 Number of alternating sign 2n+1 X 2n+1 matrices symmetric with respect to both horizontal and vertical axes (VHSASM's).

Table of values

n a(n)
0 1
1 1
2 1
3 2
4 6
5 33
6 286
7 4420
8 109820
9 4799134
10 340879665
11 42235307100
12 8564558139000
13 3012862604463000
14 1742901718473961200
15 1742218029490675762080
16 2873822682985675809192288
17 8167157387273280570395662320
18 38402596062535617548517706584760
19 310388509293255836481583597538626504

List of values

[1, 1, 1, 2, 6, 33, 286, 4420, 109820, 4799134, 340879665, 42235307100, 8564558139000, 3012862604463000, 1742901718473961200, 1742218029490675762080, 2873822682985675809192288, 8167157387273280570395662320, 38402596062535617548517706584760, 310388509293255836481583597538626504]

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

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