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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.

A213793 Number of n X n 0..1 symmetric arrays with every row summing to floor(n/2).

Table of values

n a(n)
0 1
1 1
2 2
3 4
4 18
5 112
6 1760
7 35150
8 1944530
9 133948836
10 26615510712
11 6549149852112
12 4762109992158288
13 4274712091685443584
14 11528251571501588791296
15 38295413179145036856212700
16 386860001875783390762182911250
17 4805622573099374975572752075805000

List of values

[1, 1, 2, 4, 18, 112, 1760, 35150, 1944530, 133948836, 26615510712, 6549149852112, 4762109992158288, 4274712091685443584, 11528251571501588791296, 38295413179145036856212700, 386860001875783390762182911250, 4805622573099374975572752075805000]

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

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