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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 9 |
| 4 | 84 |
| 5 | 990 |
| 6 | 14754 |
| 7 | 264600 |
| 8 | 5549424 |
| 9 | 133217784 |
| 10 | 3601384200 |
| 11 | 108249692760 |
| 12 | 3580724721672 |
| 13 | 129250420556400 |
| 14 | 5055196156459344 |
| 15 | 212951257371183240 |
| 16 | 9612027759287831040 |
| 17 | 462798880374787387200 |
| 18 | 23675607840207619145664 |
| 19 | 1282413928716141429168000 |
[1,0,2,9,84,990,14754,264600,5549424,133217784, 3601384200,108249692760,3580724721672, 129250420556400,5055196156459344, 212951257371183240,9612027759287831040, 462798880374787387200,23675607840207619145664, 1282413928716141429168000] |