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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 9 |
| 3 | 51 |
| 4 | 337 |
| 5 | 2379 |
| 6 | 17620 |
| 7 | 135112 |
| 8 | 1063645 |
| 9 | 8546809 |
| 10 | 69815202 |
| 11 | 578023750 |
| 12 | 4839738501 |
| 13 | 40910211110 |
| 14 | 348648196840 |
| 15 | 2992390437879 |
| 16 | 25842906965328 |
| 17 | 224409469141039 |
| 18 | 1958188706568797 |
| 19 | 17161676257412695 |
| 20 | 150996915954255514 |
| 21 | 1333269446351120464 |
[1,2,9,51,337,2379,17620,135112,1063645,8546809, 69815202,578023750,4839738501,40910211110, 348648196840,2992390437879,25842906965328, 224409469141039,1958188706568797, 17161676257412695,150996915954255514, 1333269446351120464] |