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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 24 |
| 5 | 60 |
| 6 | 1440 |
| 7 | 14280 |
| 8 | 120960 |
| 9 | 1905120 |
| 10 | 29937600 |
| 11 | 433762560 |
| 12 | 7823692800 |
| 13 | 155675520000 |
| 14 | 3117592558080 |
| 15 | 68545488211200 |
| 16 | 1640346727219200 |
| 17 | 40864533405696000 |
| 18 | 1079108655290265600 |
| 19 | 30355641777517056000 |
| 20 | 894726263032842240000 |
[1,0,0,6,24,60,1440,14280,120960,1905120,29937600, 433762560,7823692800,155675520000,3117592558080, 68545488211200,1640346727219200,40864533405696000, 1079108655290265600,30355641777517056000, 894726263032842240000] |