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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 8 |
| 3 | 120 |
| 4 | 672 |
| 5 | 5600 |
| 6 | 79200 |
| 7 | 50450400 |
| 8 | 201801600 |
| 9 | 10291881600 |
| 10 | 17776886400 |
| 11 | 2151003254400 |
| 12 | 3805621142400 |
| 13 | 643149973065600 |
| 14 | 643149973065600 |
| 15 | 31085582031504000 |
| 16 | 226741892465088000 |
| 17 | 65528406922410432000 |
| 18 | 31039771700089152000 |
| 19 | 414598230598090803264000 |
| 20 | 16583929223923632130560 |
[1,2,8,120,672,5600,79200,50450400,201801600, 10291881600,17776886400,2151003254400, 3805621142400,643149973065600,643149973065600, 31085582031504000,226741892465088000, 65528406922410432000,31039771700089152000, 414598230598090803264000,16583929223923632130560] |