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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 18 |
| 4 | 96 |
| 5 | 480 |
| 6 | 3600 |
| 7 | 25200 |
| 8 | 241920 |
| 9 | 2177280 |
| 10 | 25401600 |
| 11 | 279417600 |
| 12 | 3832012800 |
| 13 | 49816166400 |
| 14 | 784604620800 |
| 15 | 11769069312000 |
| 16 | 209227898880000 |
| 17 | 3556874280960000 |
| 18 | 70426110763008000 |
| 19 | 1338096104497152000 |
[1,2,6,18,96,480,3600,25200,241920,2177280, 25401600,279417600,3832012800,49816166400, 784604620800,11769069312000,209227898880000, 3556874280960000,70426110763008000, 1338096104497152000] |