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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 0 |
| 3 | 2 |
| 4 | 6 |
| 5 | 64 |
| 6 | 540 |
| 7 | 6908 |
| 8 | 93744 |
| 9 | 1542616 |
| 10 | 28057800 |
| 11 | 576840032 |
| 12 | 13029824016 |
| 13 | 323152349584 |
| 14 | 8698499671680 |
| 15 | 252998272144928 |
| 16 | 7900336700736864 |
| 17 | 263731233726459136 |
| 18 | 9370598887948893120 |
| 19 | 353114271843930110912 |
[0,1,0,2,6,64,540,6908,93744,1542616,28057800, 576840032,13029824016,323152349584,8698499671680, 252998272144928,7900336700736864, 263731233726459136,9370598887948893120, 353114271843930110912] |