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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 20 |
| 3 | 1665 |
| 4 | 356520 |
| 5 | 155809035 |
| 6 | 121055807700 |
| 7 | 152393963368875 |
| 8 | 290740199232531840 |
[1,20,1665,356520,155809035,121055807700, 152393963368875,290740199232531840] |