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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 24 |
| 5 | 240 |
| 6 | 2040 |
| 7 | 17640 |
| 8 | 202776 |
| 9 | 3066336 |
| 10 | 52446720 |
| 11 | 933636000 |
| 12 | 17416490784 |
| 13 | 350580364992 |
| 14 | 7719355635264 |
| 15 | 184232862777600 |
| 16 | 4691944607751936 |
| 17 | 126358891201529856 |
| 18 | 3591751011211717632 |
| 19 | 107772466927523060736 |
| 20 | 3408777017097439186944 |
[1,0,0,0,24,240,2040,17640,202776,3066336, 52446720,933636000,17416490784,350580364992, 7719355635264,184232862777600,4691944607751936, 126358891201529856,3591751011211717632, 107772466927523060736,3408777017097439186944] |