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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 18 |
| 4 | 209 |
| 5 | 4988 |
| 6 | 221443 |
| 7 | 19332957 |
| 8 | 3266183233 |
| 9 | 1068404830615 |
| 10 | 677798120112881 |
| 11 | 833288676199771911 |
[1,4,18,209,4988,221443,19332957,3266183233, 1068404830615,677798120112881,833288676199771911] |