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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 30 |
| 4 | 384 |
| 5 | 7480 |
| 6 | 207360 |
| 7 | 7780080 |
| 8 | 380190720 |
| 9 | 23481311616 |
| 10 | 1789201612800 |
| 11 | 164904696633600 |
| 12 | 18084647927808000 |
| 13 | 2327418985883397120 |
| 14 | 347368297708734382080 |
| 15 | 59514548453599599360000 |
| 16 | 11601363342443780505600000 |
| 17 | 2552998389393196650531225600 |
[1,1,4,30,384,7480,207360,7780080,380190720, 23481311616,1789201612800,164904696633600, 18084647927808000,2327418985883397120, 347368297708734382080,59514548453599599360000, 11601363342443780505600000, 2552998389393196650531225600] |