A147893 - OEIS

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A147893 as a simple table

n	a(n)
1	1
2	2
3	6
4	16
5	74
6	304
7	1424
8	6922
9	40922
10	250670
11	1645304
12	11152882
13	92183062
14	780194356
15	6842821428
16	61855909454

[1,2,6,16,74,304,1424,6922,40922,250670,1645304, 11152882,92183062,780194356,6842821428, 61855909454]