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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 6 |
| 5 | 18 |
| 6 | 55 |
| 7 | 147 |
| 8 | 405 |
| 9 | 1083 |
| 10 | 2961 |
| 11 | 8043 |
| 12 | 22182 |
| 13 | 61278 |
| 14 | 170883 |
| 15 | 477910 |
| 16 | 1344825 |
| 17 | 3795750 |
| 18 | 10757763 |
| 19 | 30572427 |
| 20 | 87146139 |
| 21 | 248991674 |
| 22 | 713088309 |
| 23 | 2046303339 |
| 24 | 5883410760 |
| 25 | 16944543792 |
| 26 | 48879708297 |
[0,0,1,6,18,55,147,405,1083,2961,8043,22182,61278, 170883,477910,1344825,3795750,10757763,30572427, 87146139,248991674,713088309,2046303339, 5883410760,16944543792,48879708297] |