A006786 - OEIS

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A006786 as a simple table

n	a(n)
1	1
2	2
3	4
4	8
5	18
6	44
7	117
8	351
9	1230
10	5069
11	25181
12	152045
13	1116403
14	9899865
15	104980369
16	1318017549
17	19427531763
18	333964672216
19	6660282066936

[1,2,4,8,18,44,117,351,1230,5069,25181,152045, 1116403,9899865,104980369,1318017549,19427531763, 333964672216,6660282066936]