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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 1 |
| 3 | 7 |
| 4 | 15 |
| 5 | 64 |
| 6 | 175 |
| 7 | 631 |
| 8 | 1905 |
| 9 | 6433 |
| 10 | 20224 |
| 11 | 66529 |
| 12 | 212625 |
| 13 | 692119 |
| 14 | 2226799 |
| 15 | 7217728 |
| 16 | 23284815 |
| 17 | 75343591 |
| 18 | 243328225 |
| 19 | 786800449 |
| 20 | 2542156800 |
| 21 | 8217744577 |
| 22 | 26556314401 |
| 23 | 85835882791 |
| 24 | 277405671375 |
| 25 | 896595420736 |
| 26 | 2897714688751 |
[0,1,1,7,15,64,175,631,1905,6433,20224,66529, 212625,692119,2226799,7217728,23284815,75343591, 243328225,786800449,2542156800,8217744577, 26556314401,85835882791,277405671375,896595420736, 2897714688751] |