A331505 - OEIS

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A331505 as a simple table

n	a(n)
1	1
2	1
3	3
4	15
5	45
6	455
7	1330
8	20475
9	58905
10	1221759
11	3478761
12	90858768
13	256851595
14	8093990190
15	22760723700
16	840261910995
17	2353351951665
18	99615373765775
19	278110855548955
20	13278694407181203
21	36976937738226486

[1,1,3,15,45,455,1330,20475,58905,1221759,3478761, 90858768,256851595,8093990190,22760723700, 840261910995,2353351951665,99615373765775, 278110855548955,13278694407181203, 36976937738226486]