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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 30 |
| 4 | 180 |
| 5 | 1440 |
| 6 | 12960 |
| 7 | 142560 |
| 8 | 1710720 |
| 9 | 23950080 |
| 10 | 359251200 |
| 11 | 6107270400 |
| 12 | 109930867200 |
| 13 | 2198617344000 |
| 14 | 46170964224000 |
| 15 | 1061932177152000 |
| 16 | 25486372251648000 |
| 17 | 662645678542848000 |
| 18 | 17891433320656896000 |
| 19 | 518851566299049984000 |
| 20 | 15565546988971499520000 |
| 21 | 498097503647087984640000 |
[1,2,6,30,180,1440,12960,142560,1710720,23950080, 359251200,6107270400,109930867200,2198617344000, 46170964224000,1061932177152000,25486372251648000, 662645678542848000,17891433320656896000, 518851566299049984000,15565546988971499520000, 498097503647087984640000] |