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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 36 |
| 4 | 252 |
| 5 | 2520 |
| 6 | 27720 |
| 7 | 388080 |
| 8 | 5821200 |
| 9 | 104781600 |
| 10 | 1990850400 |
| 11 | 43798708800 |
| 12 | 1007370302400 |
| 13 | 26191627862400 |
| 14 | 707173952284800 |
| 15 | 21215218568544000 |
| 16 | 657671775624864000 |
| 17 | 22360840371245376000 |
| 18 | 782629412993588160000 |
| 19 | 29739917693756350080000 |
[1,2,6,36,252,2520,27720,388080,5821200,104781600, 1990850400,43798708800,1007370302400, 26191627862400,707173952284800,21215218568544000, 657671775624864000,22360840371245376000, 782629412993588160000,29739917693756350080000] |