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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 20 |
| 3 | 1680 |
| 4 | 369600 |
| 5 | 37850400 |
| 6 | 2626916040 |
| 7 | 171548183912 |
| 8 | 12520880883034 |
| 9 | 920942694050320 |
| 10 | 65368388837752640 |
[1,1,20,1680,369600,37850400,2626916040, 171548183912,12520880883034,920942694050320, 65368388837752640] |