A020071 - OEIS

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A020071 as a simple table

n	a(n)
0	1
1	0
2	1
3	2
4	9
5	44
6	251
7	1665
8	12700
9	109544
10	1054363
11	11202616
12	130230419
13	1644159040
14	22401666926
15	327624378797
16	5119130918712
17	85105551523594
18	1499985345603353
19	27937227061862467
20	548268081089050917

[1,0,1,2,9,44,251,1665,12700,109544,1054363, 11202616,130230419,1644159040,22401666926, 327624378797,5119130918712,85105551523594, 1499985345603353,27937227061862467, 548268081089050917]