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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 27 |
| 4 | 280 |
| 5 | 4025 |
| 6 | 75876 |
| 7 | 1800253 |
| 8 | 52193408 |
| 9 | 1807302897 |
| 10 | 73406128420 |
| 11 | 3446236588421 |
| 12 | 184750419871920 |
| 13 | 11194423784630281 |
| 14 | 759960096829452260 |
| 15 | 57367378069894391325 |
| 16 | 4783586470578255085696 |
| 17 | 438054092182322814028001 |
| 18 | 43827052650093379145736900 |
[1,1,4,27,280,4025,75876,1800253,52193408, 1807302897,73406128420,3446236588421, 184750419871920,11194423784630281, 759960096829452260,57367378069894391325, 4783586470578255085696,438054092182322814028001, 43827052650093379145736900] |