A006787 - OEIS

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A006787 as a simple table

n	a(n)
1	1
2	2
3	3
4	6
5	11
6	23
7	48
8	114
9	293
10	869
11	2963
12	12066
13	58933
14	347498
15	2455693
16	20592932
17	202724920
18	2322206466
19	30743624324
20	468026657815
21	8161170076257

[1,2,3,6,11,23,48,114,293,869,2963,12066,58933, 347498,2455693,20592932,202724920,2322206466, 30743624324,468026657815,8161170076257]