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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 4 |
| 5 | 10 |
| 6 | 26 |
| 7 | 90 |
| 8 | 322 |
| 9 | 1384 |
| 10 | 6576 |
| 11 | 34870 |
| 12 | 200720 |
| 13 | 1272064 |
| 14 | 8656004 |
| 15 | 63595760 |
[1,1,2,4,10,26,90,322,1384,6576,34870,200720, 1272064,8656004,63595760] |