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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 2 |
| 4 | 6 |
| 5 | 30 |
| 6 | 270 |
| 7 | 2970 |
| 8 | 44550 |
| 9 | 757350 |
| 10 | 15904350 |
| 11 | 429417450 |
| 12 | 12453106050 |
| 13 | 435858711750 |
| 14 | 16998489758250 |
| 15 | 696938080088250 |
| 16 | 31362213603971250 |
| 17 | 1599472893802533750 |
| 18 | 91169954946744423750 |
| 19 | 5379027341857921001250 |
[0,0,2,6,30,270,2970,44550,757350,15904350, 429417450,12453106050,435858711750,16998489758250, 696938080088250,31362213603971250, 1599472893802533750,91169954946744423750, 5379027341857921001250] |