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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 1 |
| 4 | 4 |
| 5 | 5 |
| 6 | 33 |
| 7 | 139 |
| 8 | 515 |
| 9 | 1809 |
| 10 | 6181 |
| 11 | 20759 |
| 12 | 68871 |
| 13 | 226333 |
| 14 | 738089 |
| 15 | 2391459 |
| 16 | 7705867 |
| 17 | 24711977 |
| 18 | 78918957 |
| 19 | 251105839 |
[0,1,1,4,5,33,139,515,1809,6181,20759,68871, 226333,738089,2391459,7705867,24711977,78918957, 251105839] |