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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 128 |
| 3 | 2802 |
| 4 | 183220 |
| 5 | 8870150 |
| 6 | 578826040 |
| 7 | 37121438930 |
| 8 | 2639009446600 |
[2,128,2802,183220,8870150,578826040,37121438930, 2639009446600] |