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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 340 |
| 4 | 56496 |
| 5 | 28645840 |
| 6 | 20091622560 |
| 7 | 29056095714720 |
| 8 | 52981034285587200 |
| 9 | 165795456023776938240 |
[1,4,340,56496,28645840,20091622560, 29056095714720,52981034285587200, 165795456023776938240] |