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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 50 |
| 3 | 135 |
| 4 | 702 |
| 5 | 2726 |
| 6 | 11768 |
| 7 | 48526 |
| 8 | 203049 |
| 9 | 846901 |
| 10 | 3533862 |
| 11 | 14751288 |
| 12 | 61572336 |
| 13 | 256988741 |
| 14 | 1072703816 |
| 15 | 4477368403 |
| 16 | 18688452762 |
| 17 | 78005403965 |
| 18 | 325591740543 |
| 19 | 1359014862402 |
| 20 | 5672494506043 |
| 21 | 23676864307080 |
| 22 | 98826717050870 |
[2,50,135,702,2726,11768,48526,203049,846901, 3533862,14751288,61572336,256988741,1072703816, 4477368403,18688452762,78005403965,325591740543, 1359014862402,5672494506043,23676864307080, 98826717050870] |