A001997 - OEIS

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A001997 as a simple table

n	a(n)
0	1
1	1
2	2
3	4
4	10
5	24
6	66
7	176
8	493
9	1362
10	3821
11	10660
12	29864
13	83329
14	232702
15	648182
16	1804901
17	5015725
18	13931755
19	38635673
20	107090666
21	296449133
22	820271143
23	2267225157
24	6264244414
25	17291930470

[1,1,2,4,10,24,66,176,493,1362,3821,10660,29864, 83329,232702,648182,1804901,5015725,13931755, 38635673,107090666,296449133,820271143,2267225157, 6264244414,17291930470]

[1,1,2,4,10,24,66,176,493,1362,3821,10660,29864,
 83329,232702,648182,1804901,5015725,13931755,
 38635673,107090666,296449133,820271143,2267225157,
 6264244414,17291930470]