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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 6 |
| 5 | 15 |
| 6 | 44 |
| 7 | 121 |
| 8 | 353 |
| 9 | 1005 |
| 10 | 2919 |
| 11 | 8398 |
| 12 | 24310 |
| 13 | 70064 |
| 14 | 202225 |
| 15 | 582365 |
| 16 | 1676889 |
| 17 | 4821924 |
| 18 | 13857720 |
| 19 | 39787804 |
[1,1,2,6,15,44,121,353,1005,2919,8398,24310,70064, 202225,582365,1676889,4821924,13857720,39787804] |