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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 3 |
| 3 | 20 |
| 4 | 128 |
| 5 | 1269 |
| 6 | 13019 |
| 7 | 179816 |
| 8 | 2561280 |
| 9 | 45580073 |
| 10 | 831425459 |
| 11 | 18116729724 |
| 12 | 402900613376 |
| 13 | 10389410535965 |
[1,3,20,128,1269,13019,179816,2561280,45580073, 831425459,18116729724,402900613376,10389410535965] |