A222518 - OEIS

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A222518 as a simple table

n	a(n)
1	3
2	9
3	37
4	206
5	1111
6	26513
7	221659
8	6043652
9	56070649
10	1573702327
11	14644968953
12	408818223648
13	3869679949709
14	106284839137519
15	1021535069202511
16	27650305434512778
17	269672290550777351
18	7194730625200174103

[3,9,37,206,1111,26513,221659,6043652,56070649, 1573702327,14644968953,408818223648,3869679949709, 106284839137519,1021535069202511, 27650305434512778,269672290550777351, 7194730625200174103]