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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 24 |
| 3 | 200 |
| 4 | 2160 |
| 5 | 28812 |
| 6 | 458752 |
| 7 | 8503056 |
| 8 | 180000000 |
| 9 | 4287177620 |
| 10 | 113515167744 |
| 11 | 3308603804376 |
| 12 | 105288694411264 |
| 13 | 3632897460937500 |
| 14 | 135107988821114880 |
| 15 | 5388090449900829728 |
| 16 | 229385780960233586688 |
| 17 | 10383890888434362036516 |
| 18 | 498073600000000000000000 |
[1,4,24,200,2160,28812,458752,8503056,180000000, 4287177620,113515167744,3308603804376, 105288694411264,3632897460937500, 135107988821114880,5388090449900829728, 229385780960233586688,10383890888434362036516, 498073600000000000000000] |