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| n | a(n) |
|---|---|
| 1 | 20 |
| 2 | 420 |
| 3 | 160420 |
| 4 | 25600160420 |
| 5 | 655360000025600160420 |
| 6 | 429496729600000000000655360000025600160420 |
[20,420,160420,25600160420,655360000025600160420, 429496729600000000000655360000025600160420] |