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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1820 |
| 3 | 35675640 |
| 4 | 699313893460 |
| 5 | 13707950903927280 |
| 6 | 268703252919468649100 |
| 7 | 5267121150019473555730920 |
| 8 | 103246108513978467719968844740 |
| 9 | 2023830213823884774227355738862560 |
[0,1820,35675640,699313893460,13707950903927280, 268703252919468649100,5267121150019473555730920, 103246108513978467719968844740, 2023830213823884774227355738862560] |