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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 30 |
| 4 | 456 |
| 5 | 7780 |
| 6 | 150480 |
| 7 | 3279234 |
| 8 | 79775360 |
| 9 | 2146962024 |
| 10 | 63397843200 |
| 11 | 2039301671110 |
| 12 | 71007167075328 |
| 13 | 2661561062560140 |
| 14 | 106874954684266496 |
| 15 | 4577827118698118250 |
| 16 | 208369657238965616640 |
| 17 | 10044458122057793060176 |
| 18 | 511225397403604416921600 |
[0,0,2,30,456,7780,150480,3279234,79775360, 2146962024,63397843200,2039301671110, 71007167075328,2661561062560140, 106874954684266496,4577827118698118250, 208369657238965616640,10044458122057793060176, 511225397403604416921600] |