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| n | a(n) |
|---|---|
| 2 | 2 |
| 3 | 8 |
| 4 | 44 |
| 5 | 280 |
| 6 | 2040 |
| 7 | 16800 |
| 8 | 154560 |
| 9 | 1572480 |
| 10 | 17539200 |
| 11 | 212889600 |
| 12 | 2794176000 |
| 13 | 39437798400 |
| 14 | 595718323200 |
| 15 | 9589612032000 |
| 16 | 163895187456000 |
| 17 | 2964061900800000 |
| 18 | 56554301067264000 |
| 19 | 1135354270482432000 |
| 20 | 23923536413736960000 |
| 21 | 527939735774330880000 |
[2,8,44,280,2040,16800,154560,1572480,17539200, 212889600,2794176000,39437798400,595718323200, 9589612032000,163895187456000,2964061900800000, 56554301067264000,1135354270482432000, 23923536413736960000,527939735774330880000] |