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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 20 |
| 4 | 5040 |
| 5 | 2363739840 |
| 6 | 25724259347628441600 |
| 7 | 23551816324573058043308233789747587210723924136427520000 |
[0,1,20,5040,2363739840,25724259347628441600, 23551816324573058043308233789747587210723924136427\ 520000] |