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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 8 |
| 3 | 63 |
| 4 | 638 |
| 5 | 4944 |
| 6 | 107290 |
| 7 | 4122772 |
| 8 | 252553968 |
| 9 | 22777499394 |
| 10 | 2983659891399 |
| 11 | 672402701915613 |
[1,2,8,63,638,4944,107290,4122772,252553968, 22777499394,2983659891399,672402701915613] |