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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 20 |
| 3 | 280 |
| 4 | 4560 |
| 5 | 80960 |
| 6 | 1520064 |
| 7 | 29680640 |
| 8 | 596593920 |
| 9 | 12262581760 |
| 10 | 256556410880 |
| 11 | 5445566730240 |
| 12 | 116974976102400 |
| 13 | 2538140268625920 |
| 14 | 55548588652625920 |
| 15 | 1224777962595287040 |
| 16 | 27180522769369333760 |
| 17 | 606648758810237337600 |
[1,2,20,280,4560,80960,1520064,29680640,596593920, 12262581760,256556410880,5445566730240, 116974976102400,2538140268625920, 55548588652625920,1224777962595287040, 27180522769369333760,606648758810237337600] |