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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 52 |
| 3 | 1144 |
| 4 | 35464 |
| 5 | 1418560 |
| 6 | 69509440 |
| 7 | 4031547520 |
| 8 | 270113683840 |
| 9 | 20528639971840 |
| 10 | 1744934397606400 |
| 11 | 164023833375001600 |
| 12 | 16894454837625164800 |
| 13 | 1892178941814018457600 |
| 14 | 228953651959496233369600 |
| 15 | 29763974754734510338048000 |
| 16 | 4137192490908096936988672000 |
[1,4,52,1144,35464,1418560,69509440,4031547520, 270113683840,20528639971840,1744934397606400, 164023833375001600,16894454837625164800, 1892178941814018457600,228953651959496233369600, 29763974754734510338048000, 4137192490908096936988672000] |