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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 672 |
| 7 | 4128 |
| 8 | 28992 |
| 9 | 231936 |
| 10 | 2088960 |
| 11 | 20434944 |
| 12 | 221871360 |
| 13 | 2645370624 |
| 14 | 34344038400 |
| 15 | 482103767040 |
| 16 | 7269498483456 |
| 17 | 117240911729664 |
| 18 | 2013265377314688 |
| 19 | 36665783917283328 |
| 20 | 705762463906133760 |
| 21 | 14313891805008665856 |
[1,2,6,24,120,672,4128,28992,231936,2088960, 20434944,221871360,2645370624,34344038400, 482103767040,7269498483456,117240911729664, 2013265377314688,36665783917283328, 705762463906133760,14313891805008665856] |