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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 6 |
| 5 | 120 |
| 6 | 2160 |
| 7 | 41160 |
| 8 | 866460 |
| 9 | 20294064 |
| 10 | 526680000 |
| 11 | 15036999120 |
| 12 | 468848156040 |
| 13 | 15859299473160 |
| 14 | 578619457031616 |
| 15 | 22654279249875000 |
| 16 | 947570269816868880 |
| 17 | 42174922731482980320 |
| 18 | 1990416896317283627520 |
| 19 | 99290011292792071612704 |
| 20 | 5220362654145754082460000 |
[1,0,0,0,6,120,2160,41160,866460,20294064, 526680000,15036999120,468848156040,15859299473160, 578619457031616,22654279249875000, 947570269816868880,42174922731482980320, 1990416896317283627520,99290011292792071612704, 5220362654145754082460000] |