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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.

A181937 André numbers. Square array A(n,k), n>=2, k>=0, read by antidiagonals upwards, A(n,k) = n-alternating permutations of length k.

Table of values

n a(n)
0 1
1 1
2 1
3 1
4 1
5 1
6 1
7 1
8 1
9 2
10 1
11 1
12 1
13 1
14 5
15 1
16 1
17 1
18 1
19 3
20 16
21 1
22 1
23 1
24 1
25 1
26 9
27 61
28 1
29 1
30 1
31 1
32 1
33 4
34 19
35 272
36 1
37 1
38 1
39 1
40 1
41 1
42 14
43 99
44 1385
45 1
46 1
47 1
48 1
49 1
50 1
51 5
52 34
53 477
54 7936
55 1
56 1
57 1
58 1
59 1
60 1
61 1
62 20
63 69
64 1513
65 50521
66 1
67 1
68 1
69 1
70 1
71 1
72 1
73 6
74 55
75 496
76 11259
77 353792

List of values

[1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 5, 1, 1, 1, 1, 3, 16, 1, 1, 1, 1, 1, 9, 61, 1, 1, 1, 1, 1, 4, 19, 272, 1, 1, 1, 1, 1, 1, 14, 99, 1385, 1, 1, 1, 1, 1, 1, 5, 34, 477, 7936, 1, 1, 1, 1, 1, 1, 1, 20, 69, 1513, 50521, 1, 1, 1, 1, 1, 1, 1, 6, 55, 496, 11259, 353792]