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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 36 |
| 5 | 210 |
| 6 | 1350 |
| 7 | 9744 |
| 8 | 78792 |
| 9 | 708744 |
| 10 | 7036200 |
| 11 | 76521456 |
| 12 | 905507856 |
| 13 | 11589357312 |
| 14 | 159580302336 |
| 15 | 2352940786944 |
| 16 | 36994905688320 |
| 17 | 617953469022720 |
| 18 | 10929614667747840 |
| 19 | 204073497562936320 |
| 20 | 4011658382046919680 |
| 21 | 82822558521844224000 |
| 22 | 1791791417179298304000 |
[0,0,0,6,36,210,1350,9744,78792,708744,7036200, 76521456,905507856,11589357312,159580302336, 2352940786944,36994905688320,617953469022720, 10929614667747840,204073497562936320, 4011658382046919680,82822558521844224000, 1791791417179298304000] |