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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 2 |
| 2 | 45 |
| 3 | 840 |
| 4 | 23040 |
| 5 | 823680 |
| 6 | 29729700 |
| 7 | 1319205888 |
| 8 | 60949324800 |
| 9 | 3307060721664 |
| 10 | 207247208103936 |
| 11 | 13289727219664896 |
| 12 | 959973192342388224 |
| 13 | 77222763982780416000 |
| 14 | 6318019834620558704640 |
| 15 | 568402264910884213555200 |
| 16 | 52282854778694683852800000 |
[0,2,45,840,23040,823680,29729700,1319205888, 60949324800,3307060721664,207247208103936, 13289727219664896,959973192342388224, 77222763982780416000,6318019834620558704640, 568402264910884213555200, 52282854778694683852800000] |