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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 56 |
| 5 | 0 |
| 6 | 54972 |
| 7 | 764596 |
| 8 | 8972896 |
| 9 | 62560728 |
| 10 | 322246800 |
| 11 | 1323868260 |
| 12 | 4595943336 |
| 13 | 14000143196 |
| 14 | 38413461800 |
| 15 | 96746410800 |
| 16 | 226834407552 |
| 17 | 500492572112 |
| 18 | 1048044384360 |
| 19 | 2096986629308 |
| 20 | 4031211268200 |
[0,0,0,56,0,54972,764596,8972896,62560728, 322246800,1323868260,4595943336,14000143196, 38413461800,96746410800,226834407552,500492572112, 1048044384360,2096986629308,4031211268200] |