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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 64 |
| 3 | 8960 |
| 4 | 84480000 |
| 5 | 8844800000 |
| 6 | 999936000000 |
| 7 | 99999360000000 |
| 8 | 9999993600000000 |
[0,64,8960,84480000,8844800000,999936000000, 99999360000000,9999993600000000] |