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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 21 |
| 4 | 81 |
| 5 | 321 |
| 6 | 1305 |
| 7 | 5448 |
| 8 | 23177 |
| 9 | 99896 |
| 10 | 435039 |
| 11 | 1911767 |
| 12 | 8466540 |
| 13 | 37735029 |
| 14 | 169098694 |
| 15 | 761375279 |
| 16 | 3442420307 |
| 17 | 15621467912 |
| 18 | 71120379994 |
| 19 | 324737224019 |
| 20 | 1486652981107 |
| 21 | 6822074471704 |
| 22 | 31373203035946 |
| 23 | 144562584754933 |
| 24 | 667323192228423 |
| 25 | 3085581499995113 |
| 26 | 14289031592152473 |
| 27 | 66265027892766454 |
[1,2,6,21,81,321,1305,5448,23177,99896,435039, 1911767,8466540,37735029,169098694,761375279, 3442420307,15621467912,71120379994,324737224019, 1486652981107,6822074471704,31373203035946, 144562584754933,667323192228423,3085581499995113, 14289031592152473,66265027892766454] |