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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 1 |
| 3 | 6 |
| 4 | 15 |
| 5 | 55 |
| 6 | 168 |
| 7 | 559 |
| 8 | 1785 |
| 9 | 5814 |
| 10 | 18755 |
| 11 | 60787 |
| 12 | 196560 |
| 13 | 636323 |
| 14 | 2058797 |
| 15 | 6663030 |
| 16 | 21561015 |
| 17 | 69774527 |
| 18 | 225792504 |
| 19 | 730684103 |
| 20 | 2364536625 |
| 21 | 7651812246 |
| 22 | 24761766811 |
| 23 | 80130789371 |
| 24 | 259308635040 |
| 25 | 839140445275 |
| 26 | 2715515402053 |
[0,1,1,6,15,55,168,559,1785,5814,18755,60787, 196560,636323,2058797,6663030,21561015,69774527, 225792504,730684103,2364536625,7651812246, 24761766811,80130789371,259308635040,839140445275, 2715515402053] |