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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 7 |
| 3 | 20 |
| 4 | 120 |
| 5 | 2067 |
| 6 | 25754 |
| 7 | 1262771 |
| 8 | 72445170 |
| 9 | 7208056818 |
| 10 | 1634720215564 |
[1,7,20,120,2067,25754,1262771,72445170, 7208056818,1634720215564] |