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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 15 |
| 4 | 192 |
| 5 | 3450 |
| 6 | 79740 |
| 7 | 2252880 |
| 8 | 75227040 |
| 9 | 2898481320 |
| 10 | 126570502800 |
| 11 | 6177380517000 |
| 12 | 333231084648000 |
| 13 | 19687828831070400 |
| 14 | 1264341183311606400 |
| 15 | 87691200344603856000 |
| 16 | 6532556443068591936000 |
| 17 | 520205544912884502672000 |
| 18 | 44098092640676115673632000 |
| 19 | 3964782594938523231457584000 |
[1,2,15,192,3450,79740,2252880,75227040, 2898481320,126570502800,6177380517000, 333231084648000,19687828831070400, 1264341183311606400,87691200344603856000, 6532556443068591936000,520205544912884502672000, 44098092640676115673632000, 3964782594938523231457584000] |