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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 18 |
| 2 | 189 |
| 3 | 1500 |
| 4 | 9945 |
| 5 | 58014 |
| 6 | 307197 |
| 7 | 1507176 |
| 8 | 6950295 |
| 9 | 30443270 |
| 10 | 127666539 |
| 11 | 515754252 |
| 12 | 2017069431 |
| 13 | 7667214570 |
| 14 | 28419251715 |
| 15 | 102997948704 |
| 16 | 365832349542 |
| 17 | 1275914693196 |
| 18 | 4376992440590 |
[1,18,189,1500,9945,58014,307197,1507176,6950295, 30443270,127666539,515754252,2017069431, 7667214570,28419251715,102997948704,365832349542, 1275914693196,4376992440590] |