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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 15 |
| 5 | 514 |
| 6 | 106085 |
| 7 | 317848626 |
| 8 | 4238195548627 |
| 9 | 2617666555119413330 |
[0,1,2,15,514,106085,317848626,4238195548627, 2617666555119413330] |