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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 28 |
| 3 | 920 |
| 4 | 54416 |
| 5 | 5056288 |
| 6 | 678865856 |
| 7 | 124425704832 |
| 8 | 29873423298816 |
| 9 | 9104340085891584 |
| 10 | 3435702339713424384 |
| 11 | 1573394503700675106816 |
| 12 | 859935938676055185002496 |
| 13 | 553085284375423405752918016 |
[1,2,28,920,54416,5056288,678865856,124425704832, 29873423298816,9104340085891584, 3435702339713424384,1573394503700675106816, 859935938676055185002496, 553085284375423405752918016] |