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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 6 |
| 5 | 33 |
| 6 | 286 |
| 7 | 4420 |
| 8 | 109820 |
| 9 | 4799134 |
| 10 | 340879665 |
| 11 | 42235307100 |
| 12 | 8564558139000 |
| 13 | 3012862604463000 |
| 14 | 1742901718473961200 |
| 15 | 1742218029490675762080 |
| 16 | 2873822682985675809192288 |
| 17 | 8167157387273280570395662320 |
| 18 | 38402596062535617548517706584760 |
| 19 | 310388509293255836481583597538626504 |
[1,1,1,2,6,33,286,4420,109820,4799134,340879665, 42235307100,8564558139000,3012862604463000, 1742901718473961200,1742218029490675762080, 2873822682985675809192288, 8167157387273280570395662320, 38402596062535617548517706584760, 310388509293255836481583597538626504] |