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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 18 |
| 3 | 420 |
| 4 | 16200 |
| 5 | 1138320 |
| 6 | 152681760 |
| 7 | 40012315200 |
| 8 | 20727639504000 |
| 9 | 21349793828563200 |
| 10 | 43852643645542617600 |
| 11 | 179883715700853141120000 |
| 12 | 1474687052822610564537600000 |
| 13 | 24170122236238340825650936320000 |
[0,1,18,420,16200,1138320,152681760,40012315200, 20727639504000,21349793828563200, 43852643645542617600,179883715700853141120000, 1474687052822610564537600000, 24170122236238340825650936320000] |