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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 6 |
| 3 | 90 |
| 4 | 2446 |
| 5 | 105516 |
| 6 | 6624618 |
| 7 | 570683441 |
| 8 | 64611629712 |
| 9 | 9304151482673 |
| 10 | 1660908411640448 |
[1,6,90,2446,105516,6624618,570683441,64611629712, 9304151482673,1660908411640448] |