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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 0 |
| 3 | 1 |
| 4 | 2 |
| 5 | 7 |
| 6 | 31 |
| 7 | 218 |
| 8 | 2644 |
| 9 | 62286 |
| 10 | 2954024 |
| 11 | 277508807 |
| 12 | 50209732882 |
[1,1,0,1,2,7,31,218,2644,62286,2954024,277508807, 50209732882] |