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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 20 |
| 3 | 1680 |
| 4 | 362082 |
| 5 | 159459279 |
| 6 | 124951069219 |
| 7 | 158754672447498 |
| 8 | 305860462403616044 |
[1,1,20,1680,362082,159459279,124951069219, 158754672447498,305860462403616044] |