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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 6 |
| 3 | 27 |
| 4 | 432 |
| 5 | 5670 |
| 6 | 107892 |
| 7 | 2245320 |
| 8 | 55380672 |
| 9 | 1525511232 |
| 10 | 47089609200 |
| 11 | 1600308206640 |
| 12 | 59508149907456 |
| 13 | 2400782506705440 |
| 14 | 104471929620067968 |
| 15 | 4876509369382166880 |
| 16 | 243046385420037166080 |
| 17 | 12881279635221755358720 |
| 18 | 723372722620484975659008 |
[1,0,6,27,432,5670,107892,2245320,55380672, 1525511232,47089609200,1600308206640, 59508149907456,2400782506705440, 104471929620067968,4876509369382166880, 243046385420037166080,12881279635221755358720, 723372722620484975659008] |