A147257 - OEIS

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A147257 as a simple table

n	a(n)
1	1
2	1
3	1
4	1
5	1
6	5
7	17
8	39
9	137
10	661
11	3965
12	30475
13	261877
14	2593597
15	32463645
16	507974205
17	9631596681
18	224195557727
19	6341197277447
20	216685113312141
21	8987183183859385

[1,1,1,1,1,5,17,39,137,661,3965,30475,261877, 2593597,32463645,507974205,9631596681, 224195557727,6341197277447,216685113312141, 8987183183859385]