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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 60 |
| 5 | 20160 |
| 6 | 23543886643200 |
| 7 | 41101884684637603112076605638990269409595309948928000000 |
[1,2,6,60,20160,23543886643200, 41101884684637603112076605638990269409595309948928\ 000000] |