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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 3 |
| 4 | 10 |
| 5 | 20 |
| 6 | 68 |
| 7 | 185 |
| 8 | 561 |
| 9 | 1588 |
| 10 | 4814 |
| 11 | 14322 |
| 12 | 42658 |
| 13 | 127606 |
| 14 | 381695 |
| 15 | 1142358 |
| 16 | 3419569 |
| 17 | 10243325 |
| 18 | 30685488 |
| 19 | 91937645 |
| 20 | 275496007 |
| 21 | 825602377 |
| 22 | 2474298468 |
| 23 | 7415685876 |
| 24 | 22226227933 |
| 25 | 66617647655 |
| 26 | 199673303891 |
| 27 | 598488700247 |
[0,2,3,10,20,68,185,561,1588,4814,14322,42658, 127606,381695,1142358,3419569,10243325,30685488, 91937645,275496007,825602377,2474298468, 7415685876,22226227933,66617647655,199673303891, 598488700247] |