A138900 - OEIS

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A138900 as a simple table

n	a(n)
1	1
2	9
3	18
4	38
5	98
6	384
7	2580
8	2580
9	2580
10	2580
11	2580
12	367574
13	721449
14	3879720
15	3879720
16	53671968
17	53671968
18	223610114

[1,9,18,38,98,384,2580,2580,2580,2580,2580,367574, 721449,3879720,3879720,53671968,53671968, 223610114]