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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 4 |
| 3 | 8 |
| 4 | 16 |
| 5 | 80 |
| 6 | 640 |
| 7 | 4160 |
| 8 | 21760 |
| 9 | 177920 |
| 10 | 2291200 |
| 11 | 25548800 |
| 12 | 223436800 |
| 13 | 2560563200 |
| 14 | 44438118400 |
| 15 | 702660608000 |
| 16 | 8725110784000 |
| 17 | 129295622144000 |
| 18 | 2796896567296000 |
| 19 | 57197188186112000 |
| 20 | 926039081943040000 |
[1,2,4,8,16,80,640,4160,21760,177920,2291200, 25548800,223436800,2560563200,44438118400, 702660608000,8725110784000,129295622144000, 2796896567296000,57197188186112000, 926039081943040000] |