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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 66 |
| 3 | 7200 |
| 4 | 6917400 |
| 5 | 72442188000 |
| 6 | 9822893856930000 |
| 7 | 19942863749656848000000 |
| 8 | 687732249521129504041350000000 |
| 9 | 450437284567157389148103391935000000000 |
| 10 | 6194243041031315772374678081343893262937500000000 |
[1,4,66,7200,6917400,72442188000,9822893856930000, 19942863749656848000000, 687732249521129504041350000000, 450437284567157389148103391935000000000, 6194243041031315772374678081343893262937500000000] |