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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 4 |
| 3 | 16 |
| 4 | 144 |
| 5 | 768 |
| 6 | 10560 |
| 7 | 92160 |
| 8 | 1585920 |
| 9 | 21127680 |
| 10 | 419973120 |
| 11 | 7431782400 |
| 12 | 177081569280 |
| 13 | 3923981107200 |
| 14 | 105929096232960 |
| 15 | 2868863206809600 |
| 16 | 87449689674547200 |
| 17 | 2742391916199936000 |
| 18 | 94359281224797388800 |
| 19 | 3356687705428721664000 |
[1,2,4,16,144,768,10560,92160,1585920,21127680, 419973120,7431782400,177081569280,3923981107200, 105929096232960,2868863206809600, 87449689674547200,2742391916199936000, 94359281224797388800,3356687705428721664000] |