A259813 - OEIS

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A259813 as a simple table

n	a(n)
1	2
2	2
3	4
4	8
5	22
6	50
7	162
8	442
9	1590
10	4718
11	17350
12	54134
13	204324
14	669172
15	2588952
16	8805572
17	34687814
18	121539150
19	485928042

[2,2,4,8,22,50,162,442,1590,4718,17350,54134, 204324,669172,2588952,8805572,34687814,121539150, 485928042]