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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 6 |
| 3 | 34 |
| 4 | 204 |
| 5 | 1290 |
| 6 | 8486 |
| 7 | 57512 |
| 8 | 398882 |
| 9 | 2817790 |
| 10 | 20205084 |
| 11 | 146685686 |
| 12 | 1076065002 |
| 13 | 7964304176 |
| 14 | 59400014606 |
| 15 | 445991850330 |
| 16 | 3368359327020 |
| 17 | 25572325390546 |
| 18 | 195046637975486 |
| 19 | 1493883225366776 |
| 20 | 11484930879057370 |
| 21 | 88597575768631238 |
[1,1,6,34,204,1290,8486,57512,398882,2817790, 20205084,146685686,1076065002,7964304176, 59400014606,445991850330,3368359327020, 25572325390546,195046637975486,1493883225366776, 11484930879057370,88597575768631238] |