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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 4 |
| 3 | 56 |
| 4 | 996 |
| 5 | 49850 |
| 6 | 3935913 |
| 7 | 509195874 |
| 8 | 190487814086 |
| 9 | 121220201152514 |
[0,4,56,996,49850,3935913,509195874,190487814086, 121220201152514] |