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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 4 |
| 3 | 25 |
| 4 | 408 |
| 5 | 18003 |
| 6 | 2289232 |
| 7 | 797371541 |
| 8 | 652750415070 |
| 9 | 1065697211064947 |
[2,4,25,408,18003,2289232,797371541,652750415070, 1065697211064947] |