A147897 - OEIS

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A147897 as a simple table

n	a(n)
1	1
2	2
3	6
4	16
5	74
6	384
7	1970
8	10998
9	71488
10	465816
11	3856840
12	30115550
13	249292568
14	2424016580
15	22710804768
16	264711365708

[1,2,6,16,74,384,1970,10998,71488,465816,3856840, 30115550,249292568,2424016580,22710804768, 264711365708]