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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 0 |
| 3 | 6 |
| 4 | 48 |
| 5 | 180 |
| 6 | 2880 |
| 7 | 46200 |
| 8 | 483840 |
| 9 | 9087120 |
| 10 | 203212800 |
| 11 | 3752511840 |
| 12 | 89413632000 |
| 13 | 2510276408640 |
| 14 | 66301996400640 |
| 15 | 1982685238934400 |
| 16 | 67064515854336000 |
| 17 | 2274167610024710400 |
| 18 | 82881756045036748800 |
| 19 | 3301346557970183923200 |
| 20 | 135363022243685203968000 |
[1,1,0,6,48,180,2880,46200,483840,9087120, 203212800,3752511840,89413632000,2510276408640, 66301996400640,1982685238934400,67064515854336000, 2274167610024710400,82881756045036748800, 3301346557970183923200,135363022243685203968000] |