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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 2 |
| 5 | 28 |
| 6 | 394 |
| 7 | 6812 |
| 8 | 128810 |
| 9 | 2918020 |
| 10 | 83120450 |
| 11 | 2524575200 |
| 12 | 91589444450 |
| 13 | 3682730287600 |
| 14 | 155231331960250 |
| 15 | 7156139793803000 |
| 16 | 372520258834974250 |
| 17 | 21613446896458917500 |
| 18 | 1296556574981939521250 |
| 19 | 85520460088068245240000 |
| 20 | 5980843188551617897761250 |
| 21 | 430093937447553491544932500 |
[0,0,0,2,28,394,6812,128810,2918020,83120450, 2524575200,91589444450,3682730287600, 155231331960250,7156139793803000, 372520258834974250,21613446896458917500, 1296556574981939521250,85520460088068245240000, 5980843188551617897761250, 430093937447553491544932500] |