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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 1 |
| 3 | 2 |
| 4 | 4 |
| 5 | 10 |
| 6 | 25 |
| 7 | 70 |
| 8 | 201 |
| 9 | 600 |
| 10 | 1847 |
| 11 | 5830 |
| 12 | 18778 |
| 13 | 61542 |
| 14 | 204676 |
| 15 | 689411 |
| 16 | 2347970 |
| 17 | 8074762 |
| 18 | 28009676 |
| 19 | 97909318 |
| 20 | 344616322 |
| 21 | 1220539397 |
| 22 | 4347311908 |
| 23 | 15564141262 |
| 24 | 55985423060 |
| 25 | 202256970300 |
| 26 | 733607297260 |
| 27 | 2670698800614 |
| 28 | 9755982909133 |
[2,1,2,4,10,25,70,201,600,1847,5830,18778,61542, 204676,689411,2347970,8074762,28009676,97909318, 344616322,1220539397,4347311908,15564141262, 55985423060,202256970300,733607297260, 2670698800614,9755982909133] |