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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 18 |
| 2 | 864 |
| 3 | 55152 |
| 4 | 4035906 |
| 5 | 320012532 |
| 6 | 26749991016 |
| 7 | 2321220412368 |
| 8 | 207113986857024 |
| 9 | 18882911163871872 |
| 10 | 1751433553924329600 |
| 11 | 164743357888569358080 |
| 12 | 15677768071123387997040 |
| 13 | 1506728474191313049690720 |
| 14 | 146030351004313771119428160 |
| 15 | 14256607797751707815942160000 |
[1,18,864,55152,4035906,320012532,26749991016, 2321220412368,207113986857024,18882911163871872, 1751433553924329600,164743357888569358080, 15677768071123387997040,1506728474191313049690720, 146030351004313771119428160, 14256607797751707815942160000] |