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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 47 |
| 3 | 684 |
| 4 | 11010 |
| 5 | 187732 |
| 6 | 3322341 |
| 7 | 60343376 |
| 8 | 1117211474 |
| 9 | 20990977016 |
[4,47,684,11010,187732,3322341,60343376, 1117211474,20990977016] |