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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 20 |
| 3 | 1680 |
| 4 | 365640 |
| 5 | 163278207 |
| 6 | 130045765680 |
| 7 | 168183116878961 |
| 8 | 330118679949056240 |
[1,20,1680,365640,163278207,130045765680, 168183116878961,330118679949056240] |