A289709 - OEIS

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A289709 as a simple table

n	a(n)
1	2
2	4
3	10
4	28
5	84
6	272
7	946
8	3486
9	13560
10	55432
11	236852
12	1054928
13	4881972
14	23420436
15	116204016
16	595246848
17	3142169416
18	17068245184
19	95267426432
20	545732236936
21	3204607199704

[2,4,10,28,84,272,946,3486,13560,55432,236852, 1054928,4881972,23420436,116204016,595246848, 3142169416,17068245184,95267426432,545732236936, 3204607199704]