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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 12 |
| 5 | 30 |
| 6 | 120 |
| 7 | 630 |
| 8 | 19152 |
| 9 | 166320 |
| 10 | 1506600 |
| 11 | 14968800 |
| 12 | 313014240 |
| 13 | 4864860000 |
| 14 | 72829607760 |
| 15 | 1116874558800 |
| 16 | 23605893400320 |
| 17 | 495461472105600 |
| 18 | 10289649464640000 |
| 19 | 215706738207542400 |
| 20 | 5222625647551920000 |
| 21 | 133507746422859513600 |
| 22 | 3481696859911699968000 |
[1,0,0,0,12,30,120,630,19152,166320,1506600, 14968800,313014240,4864860000,72829607760, 1116874558800,23605893400320,495461472105600, 10289649464640000,215706738207542400, 5222625647551920000,133507746422859513600, 3481696859911699968000] |