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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 5 |
| 3 | 18 |
| 4 | 72 |
| 5 | 2054 |
| 6 | 53608 |
| 7 | 1744887 |
| 8 | 216103851 |
| 9 | 39184763856 |
| 10 | 11314547102638 |
| 11 | 7873316318240100 |
| 12 | 9711485486581483616 |
| 13 | 21262647899259681841579 |
[1,5,18,72,2054,53608,1744887,216103851, 39184763856,11314547102638,7873316318240100, 9711485486581483616,21262647899259681841579] |