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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 12 |
| 4 | 144 |
| 5 | 1980 |
| 6 | 31680 |
| 7 | 630840 |
| 8 | 15093120 |
| 9 | 411883920 |
| 10 | 12607660800 |
| 11 | 430740858240 |
| 12 | 16265744732160 |
| 13 | 671629503504960 |
| 14 | 30093198326231040 |
| 15 | 1454898560062147200 |
| 16 | 75503612563771392000 |
| 17 | 4186035286381024876800 |
| 18 | 246916968958719605145600 |
[1,1,2,12,144,1980,31680,630840,15093120, 411883920,12607660800,430740858240,16265744732160, 671629503504960,30093198326231040, 1454898560062147200,75503612563771392000, 4186035286381024876800,246916968958719605145600] |