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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 0 |
| 5 | 2 |
| 6 | 4 |
| 7 | 14 |
| 8 | 48 |
| 9 | 432 |
| 10 | 2316 |
| 11 | 24743 |
| 12 | 223506 |
| 13 | 2537594 |
| 14 | 26771235 |
| 15 | 344781871 |
| 16 | 3927465497 |
| 17 | 53273396228 |
| 18 | 660418431957 |
[0,0,1,0,2,4,14,48,432,2316,24743,223506,2537594, 26771235,344781871,3927465497,53273396228, 660418431957] |