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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 2 |
| 5 | 30 |
| 6 | 360 |
| 7 | 4200 |
| 8 | 50400 |
| 9 | 635040 |
| 10 | 8467200 |
| 11 | 119750400 |
| 12 | 1796256000 |
| 13 | 28540512000 |
| 14 | 479480601600 |
| 15 | 8499883392000 |
| 16 | 158664489984000 |
| 17 | 3112264995840000 |
| 18 | 64023737057280000 |
| 19 | 1378644471300096000 |
| 20 | 31019500604252160000 |
| 21 | 728045925946859520000 |
| 22 | 17796678189812121600000 |
[0,0,0,2,30,360,4200,50400,635040,8467200, 119750400,1796256000,28540512000,479480601600, 8499883392000,158664489984000,3112264995840000, 64023737057280000,1378644471300096000, 31019500604252160000,728045925946859520000, 17796678189812121600000] |