A104018 - OEIS

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A104018 as a simple table

n	a(n)
0	0
1	1
2	2
3	6
4	28
5	180
6	1448
7	13944
8	156592
9	2010000
10	29026592
11	465749856
12	8220541888
13	158283827520
14	3301678947968
15	74168218575744
16	1785106271372032
17	45828856887701760
18	1250094695454351872

[0,1,2,6,28,180,1448,13944,156592,2010000, 29026592,465749856,8220541888,158283827520, 3301678947968,74168218575744,1785106271372032, 45828856887701760,1250094695454351872]