A009697 - OEIS

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A009697 as a simple table

n	a(n)
0	0
1	1
2	2
3	7
4	20
5	117
6	518
7	4555
8	27432
9	317577
10	2405194
11	34316335
12	312554428
13	5287957053
14	56240197198
15	1099518892339
16	13369846932560
17	296443784525713
18	4056020122211730
19	100546719214082775
20	1528702557462347620

[0,1,2,7,20,117,518,4555,27432,317577,2405194, 34316335,312554428,5287957053,56240197198, 1099518892339,13369846932560,296443784525713, 4056020122211730,100546719214082775, 1528702557462347620]