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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 20 |
| 5 | 77 |
| 6 | 307 |
| 7 | 1253 |
| 8 | 5290 |
| 9 | 22909 |
| 10 | 100980 |
| 11 | 451724 |
| 12 | 2048087 |
| 13 | 9378510 |
| 14 | 43297388 |
| 15 | 201407415 |
| 16 | 942923110 |
| 17 | 4437792925 |
| 18 | 20985159916 |
| 19 | 99656902686 |
| 20 | 474991016902 |
| 21 | 2271217052157 |
| 22 | 10891974424083 |
| 23 | 52371097673100 |
| 24 | 252396679607978 |
| 25 | 1218970515610222 |
| 26 | 5898492744317845 |
| 27 | 28591972613856868 |
| 28 | 138814445398795609 |
[1,1,2,6,20,77,307,1253,5290,22909,100980,451724, 2048087,9378510,43297388,201407415,942923110, 4437792925,20985159916,99656902686,474991016902, 2271217052157,10891974424083,52371097673100, 252396679607978,1218970515610222,5898492744317845, 28591972613856868,138814445398795609] |