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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 1 |
| 5 | 4 |
| 6 | 15 |
| 7 | 35 |
| 8 | 77 |
| 9 | 226 |
| 10 | 1003 |
| 11 | 4627 |
| 12 | 22195 |
| 13 | 107764 |
| 14 | 553107 |
| 15 | 3219398 |
| 16 | 20940662 |
| 17 | 146173751 |
| 18 | 1077052928 |
[1,1,1,1,4,15,35,77,226,1003,4627,22195,107764, 553107,3219398,20940662,146173751,1077052928] |