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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 504 |
| 7 | 930 |
| 8 | 1794 |
| 9 | 3852 |
| 10 | 9246 |
| 11 | 24613 |
| 12 | 69414 |
| 13 | 185540 |
| 14 | 475520 |
| 15 | 1173888 |
| 16 | 2874864 |
| 17 | 7141844 |
| 18 | 18113441 |
| 19 | 46245953 |
| 20 | 118174785 |
| 21 | 300561681 |
| 22 | 759840542 |
| 23 | 1915350786 |
| 24 | 4833118568 |
| 25 | 12216213910 |
| 26 | 30929782130 |
| 27 | 78368738162 |
| 28 | 198501078760 |
[1,2,6,24,120,504,930,1794,3852,9246,24613,69414, 185540,475520,1173888,2874864,7141844,18113441, 46245953,118174785,300561681,759840542,1915350786, 4833118568,12216213910,30929782130,78368738162, 198501078760] |