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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 2 |
| 4 | 17 |
| 5 | 87 |
| 6 | 487 |
| 7 | 2959 |
| 8 | 18960 |
| 9 | 126997 |
| 10 | 878559 |
| 11 | 6263608 |
| 12 | 45854245 |
[0,0,2,17,87,487,2959,18960,126997,878559,6263608, 45854245] |