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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 720 |
| 3 | 31449600 |
| 4 | 444733651353600 |
| 5 | 10070314878246926155776000 |
| 6 | 614972203951464612786852376432607232000 |
[1,6,720,31449600,444733651353600, 10070314878246926155776000, 614972203951464612786852376432607232000] |