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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 2 |
| 2 | 48 |
| 3 | 1080 |
| 4 | 13440 |
| 5 | 157500 |
| 6 | 1596672 |
| 7 | 15303288 |
| 8 | 138378240 |
| 9 | 1205095320 |
| 10 | 10161580000 |
| 11 | 83564769288 |
| 12 | 672880545792 |
| 13 | 5324077540600 |
| 14 | 41500141300800 |
| 15 | 319348194300000 |
| 16 | 2430018948833280 |
| 17 | 18309616752099420 |
| 18 | 136761272555846400 |
| 19 | 1013613060373960200 |
| 20 | 7460254139738400000 |
[0,2,48,1080,13440,157500,1596672,15303288, 138378240,1205095320,10161580000,83564769288, 672880545792,5324077540600,41500141300800, 319348194300000,2430018948833280, 18309616752099420,136761272555846400, 1013613060373960200,7460254139738400000] |