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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 15 |
| 5 | 45 |
| 6 | 160 |
| 7 | 533 |
| 8 | 1785 |
| 9 | 6052 |
| 10 | 20295 |
| 11 | 68441 |
| 12 | 230400 |
| 13 | 775657 |
| 14 | 2612233 |
| 15 | 8794980 |
| 16 | 29614935 |
| 17 | 99718277 |
| 18 | 335764960 |
| 19 | 1130580029 |
| 20 | 3806834625 |
| 21 | 12818225732 |
| 22 | 43161016271 |
| 23 | 145329992177 |
| 24 | 489349324800 |
| 25 | 1647717131025 |
| 26 | 5548126370513 |
[1,1,1,4,15,45,160,533,1785,6052,20295,68441, 230400,775657,2612233,8794980,29614935,99718277, 335764960,1130580029,3806834625,12818225732, 43161016271,145329992177,489349324800, 1647717131025,5548126370513] |