A010683 - OEIS

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A010683 as a simple table

n	a(n)
0	1
1	2
2	7
3	28
4	121
5	550
6	2591
7	12536
8	61921
9	310954
10	1582791
11	8147796
12	42344121
13	221866446
14	1170747519
15	6216189936
16	33186295681
17	178034219986
18	959260792775
19	5188835909516
20	28167068630713
21	153395382655222

[1,2,7,28,121,550,2591,12536,61921,310954,1582791, 8147796,42344121,221866446,1170747519,6216189936, 33186295681,178034219986,959260792775, 5188835909516,28167068630713,153395382655222]