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| n | a(n) |
|---|---|
| 2 | 1 |
| 3 | 2 |
| 4 | 6 |
| 5 | 20 |
| 6 | 80 |
| 7 | 366 |
| 8 | 1897 |
| 9 | 10976 |
| 10 | 70155 |
| 11 | 490930 |
| 12 | 3733246 |
| 13 | 30655152 |
| 14 | 270334766 |
| 15 | 2548153230 |
| 16 | 25566585450 |
| 17 | 272052199520 |
| 18 | 3060191748695 |
| 19 | 36282298766760 |
| 20 | 452220051658265 |
| 21 | 5911274512571280 |
| 22 | 80862988937379390 |
| 23 | 1155309461910323610 |
| 24 | 17208404375488550100 |
[1,2,6,20,80,366,1897,10976,70155,490930,3733246, 30655152,270334766,2548153230,25566585450, 272052199520,3060191748695,36282298766760, 452220051658265,5911274512571280, 80862988937379390,1155309461910323610, 17208404375488550100] |