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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 20 |
| 6 | 240 |
| 7 | 1260 |
| 8 | 5600 |
| 9 | 45360 |
| 10 | 383040 |
| 11 | 2451680 |
| 12 | 17128320 |
| 13 | 157769040 |
| 14 | 1902380480 |
| 15 | 18882623760 |
| 16 | 163633317120 |
| 17 | 2095059774080 |
| 18 | 30792478993920 |
| 19 | 346562329685760 |
| 20 | 3905491275514880 |
| 21 | 58609449249207360 |
| 22 | 866031730098205440 |
[0,0,0,0,0,20,240,1260,5600,45360,383040,2451680, 17128320,157769040,1902380480,18882623760, 163633317120,2095059774080,30792478993920, 346562329685760,3905491275514880, 58609449249207360,866031730098205440] |