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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 131 |
| 5 | 2261 |
| 6 | 68915 |
| 7 | 3936847 |
| 8 | 398896240 |
| 9 | 73105887206 |
| 10 | 24124756465130 |
[1,4,12,131,2261,68915,3936847,398896240, 73105887206,24124756465130] |