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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 3 |
| 4 | 20 |
| 5 | 244 |
| 6 | 6891 |
| 7 | 378813 |
| 8 | 47917598 |
| 9 | 12118420172 |
| 10 | 6998287399637 |
[0,1,3,20,244,6891,378813,47917598,12118420172, 6998287399637] |