A189568 - OEIS

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A189568 as a simple table

n	a(n)
0	1
1	1
2	2
3	6
4	24
5	80
6	326
7	1566
8	9544
9	65036
10	518498
11	4750006
12	48830634
13	554929274
14	6926227324
15	93970452970
16	1377573324202

[1,1,2,6,24,80,326,1566,9544,65036,518498,4750006, 48830634,554929274,6926227324,93970452970, 1377573324202]