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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 36 |
| 5 | 270 |
| 6 | 2520 |
| 7 | 28560 |
| 8 | 361200 |
| 9 | 5481000 |
| 10 | 88565400 |
| 11 | 1654052400 |
| 12 | 32885455680 |
| 13 | 721400359680 |
| 14 | 17024709461760 |
| 15 | 429108154675200 |
| 16 | 11721695953968000 |
| 17 | 333806974560259200 |
| 18 | 10358856500289897600 |
| 19 | 331148326165228091520 |
| 20 | 11429645706428485536000 |
| 21 | 407641141014720316704000 |
[1,2,6,36,270,2520,28560,361200,5481000,88565400, 1654052400,32885455680,721400359680, 17024709461760,429108154675200,11721695953968000, 333806974560259200,10358856500289897600, 331148326165228091520,11429645706428485536000, 407641141014720316704000] |