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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 36 |
| 5 | 160 |
| 6 | 1620 |
| 7 | 18648 |
| 8 | 220080 |
| 9 | 2924640 |
| 10 | 44775360 |
| 11 | 753207840 |
| 12 | 13836731040 |
| 13 | 276442882560 |
| 14 | 5972081379264 |
| 15 | 138607594171200 |
| 16 | 3440465206214400 |
| 17 | 90951997553464320 |
| 18 | 2551374460670538240 |
| 19 | 75694365919478960640 |
| 20 | 2368107785432883916800 |
[1,0,0,6,36,160,1620,18648,220080,2924640, 44775360,753207840,13836731040,276442882560, 5972081379264,138607594171200,3440465206214400, 90951997553464320,2551374460670538240, 75694365919478960640,2368107785432883916800] |