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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 15 |
| 3 | 131325321 |
| 4 | 210449029945495266124836624698709415244045199778210143675 |
[1,15,131325321, 21044902994549526612483662469870941524404519977821\ 0143675] |