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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 96 |
| 4 | 784 |
| 5 | 6498 |
| 6 | 50962 |
| 7 | 378380 |
| 8 | 2744000 |
| 9 | 19498404 |
| 10 | 136375750 |
| 11 | 942366144 |
| 12 | 6447489300 |
| 13 | 43752057470 |
| 14 | 294860178246 |
| 15 | 1975527311278 |
| 16 | 13168916586328 |
| 17 | 87397738603826 |
| 18 | 577783360045754 |
| 19 | 3806594222800152 |
| 20 | 25002061781815280 |
[0,2,96,784,6498,50962,378380,2744000,19498404, 136375750,942366144,6447489300,43752057470, 294860178246,1975527311278,13168916586328, 87397738603826,577783360045754,3806594222800152, 25002061781815280] |