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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 0 |
| 5 | 60 |
| 6 | 360 |
| 7 | 840 |
| 8 | 20160 |
| 9 | 75600 |
| 10 | 1058400 |
| 11 | 10311840 |
| 12 | 79833600 |
| 13 | 1305944640 |
| 14 | 11018367360 |
| 15 | 174616041600 |
| 16 | 2150397849600 |
| 17 | 28661419987200 |
| 18 | 473667677683200 |
| 19 | 6293779652160000 |
| 20 | 114484773731328000 |
| 21 | 1766543101087564800 |
| 22 | 31640707215390873600 |
[1,0,0,6,0,60,360,840,20160,75600,1058400, 10311840,79833600,1305944640,11018367360, 174616041600,2150397849600,28661419987200, 473667677683200,6293779652160000, 114484773731328000,1766543101087564800, 31640707215390873600] |