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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 20 |
| 5 | 83 |
| 6 | 410 |
| 7 | 2109 |
| 8 | 11097 |
| 9 | 59698 |
| 10 | 325240 |
| 11 | 1786820 |
| 12 | 9888567 |
| 13 | 55061514 |
| 14 | 308166631 |
| 15 | 1732444205 |
| 16 | 9777801332 |
| 17 | 55377818912 |
| 18 | 314616215640 |
| 19 | 1792424007975 |
| 20 | 10237590562396 |
| 21 | 58607205582421 |
| 22 | 336211631539125 |
| 23 | 1932440491804486 |
[1,2,6,20,83,410,2109,11097,59698,325240,1786820, 9888567,55061514,308166631,1732444205,9777801332, 55377818912,314616215640,1792424007975, 10237590562396,58607205582421,336211631539125, 1932440491804486] |