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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 80640 |
| 3 | 516287415629905920000 |
| 4 | 135851139773030831011345707357554182190215987200000000000 |
[1,2,80640,516287415629905920000, 13585113977303083101134570735755418219021598720000\ 0000000] |