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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.

A195522 T(n,k) = Number of lower triangles of an n X n -k..k array with all row and column sums zero.

Table of values

n a(n)
1 1
2 1
3 1
4 1
5 1
6 3
7 1
8 1
9 5
10 15
11 1
12 1
13 7
14 65
15 199
16 1
17 1
18 9
19 175
20 3753
21 6247
22 1
23 1
24 11
25 369
26 27267
27 860017
28 505623
29 1
30 1
31 13
32 671
33 121367
34 23663523
35 839301197
36 105997283
37 1
38 1
39 15
40 1105
41 401565
42 286168923
43 122092290831
44 3535646416019
45 58923059879
46 1
47 1
48 17

List of values

[1, 1, 1, 1, 1, 3, 1, 1, 5, 15, 1, 1, 7, 65, 199, 1, 1, 9, 175, 3753, 6247, 1, 1, 11, 369, 27267, 860017, 505623, 1, 1, 13, 671, 121367, 23663523, 839301197, 105997283, 1, 1, 15, 1105, 401565, 286168923, 122092290831, 3535646416019, 58923059879, 1, 1, 17]