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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 0 |
| 6 | 720 |
| 7 | 5040 |
| 8 | 23520 |
| 9 | 90720 |
| 10 | 312480 |
| 11 | 997920 |
| 12 | 3017520 |
| 13 | 8751600 |
| 14 | 24552528 |
| 15 | 67026960 |
| 16 | 178825920 |
| 17 | 467812800 |
| 18 | 1203094080 |
| 19 | 3048024384 |
| 20 | 7620293520 |
[0,0,0,0,0,0,720,5040,23520,90720,312480,997920, 3017520,8751600,24552528,67026960,178825920, 467812800,1203094080,3048024384,7620293520] |