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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 2240421120000 |
| 3 | 2357018782335863659143506877669927151046989269393693317529600000000000000 |
[1,4,2240421120000, 23570187823358636591435068776699271510469892693936\ 93317529600000000000000] |