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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 30 |
| 5 | 391 |
| 6 | 9400 |
| 7 | 398140 |
| 8 | 30500696 |
| 9 | 4161339596 |
| 10 | 1058339281896 |
| 11 | 515295969951016 |
[1,1,1,4,30,391,9400,398140,30500696,4161339596, 1058339281896,515295969951016] |