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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 23 |
| 4 | 959 |
| 5 | 126733 |
| 6 | 52618569 |
| 7 | 64233268442 |
| 8 | 231757210785889 |
| 9 | 2449990554327149088 |
[1,4,23,959,126733,52618569,64233268442, 231757210785889,2449990554327149088] |