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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 2 |
| 5 | 6 |
| 6 | 65 |
| 7 | 560 |
| 8 | 6939 |
| 9 | 89952 |
| 10 | 1372469 |
| 11 | 22986721 |
| 12 | 423073642 |
| 13 | 8439627699 |
[1,1,2,2,6,65,560,6939,89952,1372469,22986721, 423073642,8439627699] |