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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 21 |
| 5 | 71 |
| 6 | 260 |
| 7 | 1000 |
| 8 | 3953 |
| 9 | 15917 |
| 10 | 65410 |
| 11 | 273438 |
| 12 | 1157570 |
| 13 | 4949533 |
| 14 | 21375685 |
| 15 | 93089976 |
| 16 | 408147676 |
| 17 | 1800678253 |
| 18 | 7989131978 |
| 19 | 35618243432 |
| 20 | 159490955535 |
| 21 | 717004472555 |
| 22 | 3234915611753 |
| 23 | 14642248373759 |
| 24 | 66471250888687 |
| 25 | 302578116535178 |
| 26 | 1380765732673355 |
| 27 | 6315304036774097 |
| 28 | 28945896397033450 |
[1,1,2,6,21,71,260,1000,3953,15917,65410,273438, 1157570,4949533,21375685,93089976,408147676, 1800678253,7989131978,35618243432,159490955535, 717004472555,3234915611753,14642248373759, 66471250888687,302578116535178,1380765732673355, 6315304036774097,28945896397033450] |