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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 36 |
| 5 | 210 |
| 6 | 3870 |
| 7 | 70224 |
| 8 | 1122072 |
| 9 | 23086344 |
| 10 | 586910880 |
| 11 | 15469437456 |
| 12 | 441107126856 |
| 13 | 14206113541152 |
| 14 | 496333927370736 |
| 15 | 18463733657766144 |
| 16 | 739328759822848320 |
| 17 | 31759148433997889280 |
| 18 | 1447876893211813379520 |
| 19 | 69881726567495477445120 |
[1,0,0,6,36,210,3870,70224,1122072,23086344, 586910880,15469437456,441107126856,14206113541152, 496333927370736,18463733657766144, 739328759822848320,31759148433997889280, 1447876893211813379520,69881726567495477445120] |