A261539 - OEIS

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A261539 as a simple table

n	a(n)
1	0
2	1
3	2
4	3
5	6
6	9
7	12
8	21
9	42
10	150
11	195
12	390
13	411
14	1215
15	2754
16	2757
17	3246
18	6186
19	11340
20	12885
21	84708
22	87120
23	191772
24	503919
25	786441

[0,1,2,3,6,9,12,21,42,150,195,390,411,1215,2754, 2757,3246,6186,11340,12885,84708,87120,191772, 503919,786441]