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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 24 |
| 5 | 0 |
| 6 | 2520 |
| 7 | 40320 |
| 8 | 181440 |
| 9 | 6048000 |
| 10 | 219542400 |
| 11 | 2874009600 |
| 12 | 57340483200 |
| 13 | 2847824179200 |
| 14 | 73556683200000 |
| 15 | 1606870263398400 |
| 16 | 77095250039808000 |
| 17 | 3111553620983808000 |
| 18 | 91548244100875161600 |
| 19 | 4054836680294400000000 |
| 20 | 210947475222439667712000 |
| 21 | 8463340108487290650624000 |
| 22 | 381818416967499733917696000 |
[1,0,0,6,24,0,2520,40320,181440,6048000,219542400, 2874009600,57340483200,2847824179200, 73556683200000,1606870263398400,77095250039808000, 3111553620983808000,91548244100875161600, 4054836680294400000000,210947475222439667712000, 8463340108487290650624000, 381818416967499733917696000] |