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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 9 |
| 4 | 48 |
| 5 | 200 |
| 6 | 1440 |
| 7 | 8820 |
| 8 | 80640 |
| 9 | 653184 |
| 10 | 7257600 |
| 11 | 73180800 |
| 12 | 958003200 |
| 13 | 11564467200 |
| 14 | 174356582400 |
| 15 | 2451889440000 |
| 16 | 41845579776000 |
| 17 | 671854030848000 |
| 18 | 12804747411456000 |
| 19 | 231125690776780800 |
| 20 | 4865804016353280000 |
[1,4,9,48,200,1440,8820,80640,653184,7257600, 73180800,958003200,11564467200,174356582400, 2451889440000,41845579776000,671854030848000, 12804747411456000,231125690776780800, 4865804016353280000] |