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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 24 |
| 4 | 120 |
| 5 | 840 |
| 6 | 7560 |
| 7 | 83160 |
| 8 | 1081080 |
| 9 | 17297280 |
| 10 | 294053760 |
| 11 | 5587021440 |
| 12 | 128501493120 |
| 13 | 3212537328000 |
| 14 | 93163582512000 |
| 15 | 2888071057872000 |
| 16 | 106858629141264000 |
| 17 | 4381203794791824000 |
| 18 | 184010559381256608000 |
| 19 | 7912454053394034144000 |
| 20 | 371885340509519604768000 |
[1,2,6,24,120,840,7560,83160,1081080,17297280, 294053760,5587021440,128501493120,3212537328000, 93163582512000,2888071057872000, 106858629141264000,4381203794791824000, 184010559381256608000,7912454053394034144000, 371885340509519604768000] |