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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 18 |
| 4 | 55 |
| 5 | 173 |
| 6 | 560 |
| 7 | 1858 |
| 8 | 6291 |
| 9 | 21657 |
| 10 | 75581 |
| 11 | 266797 |
| 12 | 950911 |
| 13 | 3417339 |
| 14 | 12369284 |
| 15 | 45052514 |
| 16 | 165002459 |
| 17 | 607283489 |
| 18 | 2244901889 |
| 19 | 8331383609 |
| 20 | 31030387439 |
| 21 | 115948830659 |
| 22 | 434542177289 |
| 23 | 1632963760973 |
| 24 | 6151850548775 |
| 25 | 23229299473603 |
| 26 | 87900903988155 |
[1,2,6,18,55,173,560,1858,6291,21657,75581,266797, 950911,3417339,12369284,45052514,165002459, 607283489,2244901889,8331383609,31030387439, 115948830659,434542177289,1632963760973, 6151850548775,23229299473603,87900903988155] |