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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 24 |
| 5 | 60 |
| 6 | 840 |
| 7 | 10290 |
| 8 | 80976 |
| 9 | 847224 |
| 10 | 13306320 |
| 11 | 190271070 |
| 12 | 2677088040 |
| 13 | 46082426676 |
| 14 | 874515884424 |
| 15 | 16582066303530 |
| 16 | 336875275380000 |
| 17 | 7539189088358640 |
| 18 | 176554878235711776 |
| 19 | 4295134487197296054 |
| 20 | 111114287924643309240 |
| 21 | 3036073975138066955820 |
[1,0,0,6,24,60,840,10290,80976,847224,13306320, 190271070,2677088040,46082426676,874515884424, 16582066303530,336875275380000,7539189088358640, 176554878235711776,4295134487197296054, 111114287924643309240,3036073975138066955820] |