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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 8 |
| 3 | 48 |
| 4 | 320 |
| 5 | 1888 |
| 6 | 11648 |
| 7 | 69504 |
| 8 | 419840 |
| 9 | 2515456 |
| 10 | 15116288 |
| 11 | 90667008 |
| 12 | 544194560 |
| 13 | 3264913408 |
| 14 | 19591036928 |
| 15 | 117544157184 |
| 16 | 705277460480 |
| 17 | 4231648116736 |
| 18 | 25389989101568 |
| 19 | 152339800915968 |
| 20 | 914039609753600 |
| 21 | 5484236586876928 |
[1,8,48,320,1888,11648,69504,419840,2515456, 15116288,90667008,544194560,3264913408, 19591036928,117544157184,705277460480, 4231648116736,25389989101568,152339800915968, 914039609753600,5484236586876928] |