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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 40 |
| 3 | 908 |
| 4 | 10989 |
| 5 | 139233 |
| 6 | 1782679 |
| 7 | 22578152 |
| 8 | 286030234 |
| 9 | 3627899762 |
[4,40,908,10989,139233,1782679,22578152,286030234, 3627899762] |