A008987 - OEIS

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A008987 as a simple table

n	a(n)
0	1
1	1
2	2
3	6
4	21
5	99
6	588
7	3829
8	27404
9	206543
10	1626638
11	13242275
12	110865868
13	950078474
14	8307074080
15	73908443799
16	667684486429

[1,1,2,6,21,99,588,3829,27404,206543,1626638, 13242275,110865868,950078474,8307074080, 73908443799,667684486429]