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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 3 |
| 4 | 6 |
| 5 | 25 |
| 6 | 180 |
| 7 | 1281 |
| 8 | 10010 |
| 9 | 90063 |
| 10 | 902790 |
| 11 | 9929755 |
| 12 | 119134224 |
| 13 | 1548768585 |
| 14 | 21683033372 |
| 15 | 325245031125 |
| 16 | 5203916869710 |
| 17 | 88466595897631 |
| 18 | 1592398778725710 |
| 19 | 30255576613653483 |
| 20 | 605111531456405960 |
| 21 | 12707342164389159945 |
| 22 | 279561527629906821684 |
[0,0,0,3,6,25,180,1281,10010,90063,902790,9929755, 119134224,1548768585,21683033372,325245031125, 5203916869710,88466595897631,1592398778725710, 30255576613653483,605111531456405960, 12707342164389159945,279561527629906821684] |