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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 6 |
| 3 | 6 |
| 4 | 90 |
| 5 | 180 |
| 6 | 1770 |
| 7 | 5040 |
| 8 | 39690 |
| 9 | 140280 |
| 10 | 964656 |
| 11 | 3922380 |
| 12 | 24755346 |
| 13 | 110486376 |
| 14 | 660153780 |
| 15 | 3137330196 |
| 16 | 18103340970 |
| 17 | 89794566576 |
| 18 | 506892467796 |
| 19 | 2589310074780 |
| 20 | 14419819659960 |
| 21 | 75181803891480 |
| 22 | 415298937771900 |
| 23 | 2196704341517400 |
| 24 | 12078576672927570 |
[1,0,6,6,90,180,1770,5040,39690,140280,964656, 3922380,24755346,110486376,660153780,3137330196, 18103340970,89794566576,506892467796, 2589310074780,14419819659960,75181803891480, 415298937771900,2196704341517400, 12078576672927570] |