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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 3 |
| 3 | 8 |
| 4 | 48 |
| 5 | 121 |
| 6 | 312 |
| 7 | 16104 |
| 8 | 122640 |
| 9 | 7596480 |
| 10 | 61171656 |
| 11 | 4093181688 |
| 12 | 2366564736720 |
| 13 | 19924948267224 |
| 14 | 12169835294351280 |
| 15 | 889585277491970400 |
| 16 | 7633882962663652968 |
| 17 | 565719454445904325272 |
| 18 | 365721616371321130128240 |
| 19 | 239498069351503974657030696 |
| 20 | 2084811062715550992506283600 |
[0,3,8,48,121,312,16104,122640,7596480,61171656, 4093181688,2366564736720,19924948267224, 12169835294351280,889585277491970400, 7633882962663652968,565719454445904325272, 365721616371321130128240, 239498069351503974657030696, 2084811062715550992506283600] |