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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 30 |
| 5 | 120 |
| 6 | 455 |
| 7 | 1708 |
| 8 | 6426 |
| 9 | 24300 |
| 10 | 92367 |
| 11 | 352704 |
| 12 | 1352065 |
| 13 | 5200286 |
| 14 | 20058285 |
| 15 | 77558744 |
| 16 | 300540178 |
| 17 | 1166803092 |
| 18 | 4537567631 |
| 19 | 17672631880 |
| 20 | 68923264389 |
| 21 | 269128937198 |
| 22 | 1052049481837 |
| 23 | 4116715363776 |
| 24 | 16123801841525 |
| 25 | 63205303218850 |
| 26 | 247959266474025 |
| 27 | 973469712824028 |
[0,0,6,30,120,455,1708,6426,24300,92367,352704, 1352065,5200286,20058285,77558744,300540178, 1166803092,4537567631,17672631880,68923264389, 269128937198,1052049481837,4116715363776, 16123801841525,63205303218850,247959266474025, 973469712824028] |