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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 48 |
| 3 | 452 |
| 4 | 4680 |
| 5 | 51504 |
| 6 | 591312 |
| 7 | 7002864 |
| 8 | 84926304 |
| 9 | 1049402944 |
| 10 | 13165069824 |
| 11 | 167239042176 |
| 12 | 2146912312064 |
| 13 | 27808372643328 |
| 14 | 362981425115904 |
| 15 | 4769884412086016 |
| 16 | 63050983340533248 |
| 17 | 837805424714425344 |
| 18 | 11184489029495865344 |
| 19 | 149935005483457542144 |
| 20 | 2017560365768892739584 |
[1,6,48,452,4680,51504,591312,7002864,84926304, 1049402944,13165069824,167239042176,2146912312064, 27808372643328,362981425115904,4769884412086016, 63050983340533248,837805424714425344, 11184489029495865344,149935005483457542144, 2017560365768892739584] |