A089427 - OEIS

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A089427 as a simple table

n	a(n)
0	1
1	1
2	1
3	3
4	4
5	18
6	33
7	161
8	433
9	1705
10	10789
11	29157
12	88720
13	490289
14	1881309
15	4731356
16	17455195
17	36595263
18	178053588
19	405917904
20	3256229459

[1,1,1,3,4,18,33,161,433,1705,10789,29157,88720, 490289,1881309,4731356,17455195,36595263, 178053588,405917904,3256229459]