A129815 - OEIS

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A129815 as a simple table

n	a(n)
1	0
2	0
3	1
4	2
5	6
6	22
7	102
8	506
9	2952
10	18502
11	131112
12	991226
13	8271792
14	73176262
15	703077552
16	7121578106
17	77437418112
18	883521487942
19	10726837356672
20	136104948161786
21	1825110309733632

[0,0,1,2,6,22,102,506,2952,18502,131112,991226, 8271792,73176262,703077552,7121578106,77437418112, 883521487942,10726837356672,136104948161786, 1825110309733632]