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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 36 |
| 5 | 180 |
| 6 | 1260 |
| 7 | 7560 |
| 8 | 25200 |
| 9 | 277200 |
| 10 | 1663200 |
| 11 | 21621600 |
| 12 | 64864800 |
| 13 | 735134400 |
| 14 | 6983776800 |
| 15 | 146659312800 |
| 16 | 1613252440800 |
| 17 | 37104806138400 |
| 18 | 445257673660800 |
| 19 | 4452576736608000 |
| 20 | 38588998383936000 |
| 21 | 1080491954750208000 |
[1,4,12,36,180,1260,7560,25200,277200,1663200, 21621600,64864800,735134400,6983776800, 146659312800,1613252440800,37104806138400, 445257673660800,4452576736608000, 38588998383936000,1080491954750208000] |