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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 30 |
| 5 | 180 |
| 6 | 1260 |
| 7 | 10080 |
| 8 | 93240 |
| 9 | 1015560 |
| 10 | 12146400 |
| 11 | 158004000 |
| 12 | 2226193200 |
| 13 | 34162128000 |
| 14 | 565750785600 |
| 15 | 10034584560000 |
| 16 | 190820565936000 |
| 17 | 3845407181616000 |
| 18 | 81995523626016000 |
| 19 | 1844123531009760000 |
| 20 | 43689721287532320000 |
| 21 | 1086745683839175360000 |
[1,1,2,6,30,180,1260,10080,93240,1015560,12146400, 158004000,2226193200,34162128000,565750785600, 10034584560000,190820565936000,3845407181616000, 81995523626016000,1844123531009760000, 43689721287532320000,1086745683839175360000] |