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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 120 |
| 6 | 1800 |
| 7 | 16800 |
| 8 | 126000 |
| 9 | 834120 |
| 10 | 5102880 |
| 11 | 29607600 |
| 12 | 165526200 |
| 13 | 901020120 |
| 14 | 4808987400 |
| 15 | 25292030280 |
| 16 | 131542740000 |
| 17 | 678330198120 |
| 18 | 3474970629480 |
| 19 | 17710714165200 |
| 20 | 89904725757000 |
[0,0,0,0,120,1800,16800,126000,834120,5102880, 29607600,165526200,901020120,4808987400, 25292030280,131542740000,678330198120, 3474970629480,17710714165200,89904725757000] |