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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 21 |
| 5 | 183 |
| 6 | 1918 |
| 7 | 22892 |
| 8 | 290123 |
| 9 | 3836377 |
| 10 | 52291348 |
| 11 | 730272739 |
[1,1,4,21,183,1918,22892,290123,3836377,52291348, 730272739] |