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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 6 |
| 5 | 30 |
| 6 | 120 |
| 7 | 1560 |
| 8 | 10920 |
| 9 | 185640 |
| 10 | 2042040 |
| 11 | 181741560 |
| 12 | 1090449360 |
| 13 | 254074700880 |
| 14 | 7368166325520 |
| 15 | 449458145856720 |
| 16 | 21124532855265840 |
| 17 | 33735878969859546480 |
| 18 | 640981700427331383120 |
| 19 | 2679944489486672512824720 |
| 20 | 109877724068953573025813520 |
[1,1,2,6,30,120,1560,10920,185640,2042040, 181741560,1090449360,254074700880,7368166325520, 449458145856720,21124532855265840, 33735878969859546480,640981700427331383120, 2679944489486672512824720, 109877724068953573025813520] |