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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 1080 |
| 7 | 10080 |
| 8 | 120960 |
| 9 | 1874880 |
| 10 | 34473600 |
| 11 | 738460800 |
| 12 | 17982518400 |
| 13 | 489858969600 |
| 14 | 14834839219200 |
| 15 | 498452777222400 |
| 16 | 18583796335104000 |
| 17 | 768773914900992000 |
| 18 | 35220800475250790400 |
| 19 | 1779227869201400217600 |
| 20 | 98469904378626772992000 |
[1,0,0,6,24,120,1080,10080,120960,1874880, 34473600,738460800,17982518400,489858969600, 14834839219200,498452777222400,18583796335104000, 768773914900992000,35220800475250790400, 1779227869201400217600,98469904378626772992000] |