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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 25 |
| 4 | 239 |
| 5 | 9456 |
| 6 | 423328 |
| 7 | 55900189 |
| 8 | 15136412831 |
| 9 | 8243506243585 |
[1,4,25,239,9456,423328,55900189,15136412831, 8243506243585] |