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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | 4 |
| 4 | 18 |
| 5 | 111 |
| 6 | 948 |
| 7 | 12117 |
| 8 | 248598 |
| 9 | 8729910 |
| 10 | 546656296 |
| 11 | 62211632285 |
| 12 | 12971518524320 |
| 13 | 4978986704302097 |
| 14 | 3532978161315634913 |
| 15 | 4653469892186977002460 |
| 16 | 11423275400784921191855736 |
| 17 | 52462085466397337031539370710 |
| 18 | 452380601683401136290499567383958 |
[0,0,1,4,18,111,948,12117,248598,8729910, 546656296,62211632285,12971518524320, 4978986704302097,3532978161315634913, 4653469892186977002460,11423275400784921191855736, 52462085466397337031539370710, 452380601683401136290499567383958] |