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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 72 |
| 5 | 840 |
| 6 | 12780 |
| 7 | 238770 |
| 8 | 5281920 |
| 9 | 134946000 |
| 10 | 3909578400 |
| 11 | 126638542800 |
| 12 | 4535037460800 |
| 13 | 177904622095200 |
| 14 | 7586967310322400 |
| 15 | 349479111223242000 |
| 16 | 17292052928037888000 |
| 17 | 914673660594613920000 |
| 18 | 51506610632458293312000 |
| 19 | 3076341001739003430432000 |
[1,2,9,72,840,12780,238770,5281920,134946000, 3909578400,126638542800,4535037460800, 177904622095200,7586967310322400, 349479111223242000,17292052928037888000, 914673660594613920000,51506610632458293312000, 3076341001739003430432000] |