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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 6 |
| 3 | 48 |
| 4 | 496 |
| 5 | 6240 |
| 6 | 91776 |
| 7 | 1537088 |
| 8 | 28798464 |
| 9 | 595955520 |
| 10 | 13491708800 |
| 11 | 331623830208 |
| 12 | 8795579682048 |
| 13 | 250414554029120 |
| 14 | 7618664812010112 |
| 15 | 246723028123216320 |
| 16 | 8474819292528368640 |
| 17 | 307805848056790016832 |
| 18 | 11787380650768137830784 |
| 19 | 474716135626387606640832 |
| 20 | 20058947200327244710705920 |
[1,1,6,48,496,6240,91776,1537088,28798464, 595955520,13491708800,331623830208,8795579682048, 250414554029120,7618664812010112, 246723028123216320,8474819292528368640, 307805848056790016832,11787380650768137830784, 474716135626387606640832, 20058947200327244710705920] |