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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 4 |
| 5 | 56 |
| 6 | 9408 |
| 7 | 16942080 |
| 8 | 535281401856 |
| 9 | 377597570964258816 |
| 10 | 7580721483160132811489280 |
| 11 | 5363937773277371298119673540771840 |
[1,1,1,4,56,9408,16942080,535281401856, 377597570964258816,7580721483160132811489280, 5363937773277371298119673540771840] |