A273754 - OEIS

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A273754 as a simple table

n	a(n)
1	1
2	1
3	1
4	2
5	3
6	8
7	18
8	70
9	180
10	770
11	2610
12	14570
13	54720
14	330960
15	1562814
16	11946080
17	57126780
18	429542960
19	2465050968
20	22517159760

[1,1,1,2,3,8,18,70,180,770,2610,14570,54720, 330960,1562814,11946080,57126780,429542960, 2465050968,22517159760]