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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 8 |
| 4 | 45 |
| 5 | 504 |
| 6 | 5040 |
| 7 | 86400 |
| 8 | 1247400 |
| 9 | 28828800 |
| 10 | 544864320 |
| 11 | 15850598400 |
| 12 | 370507737600 |
| 13 | 12996271411200 |
| 14 | 362038989312000 |
| 15 | 14867734494412800 |
| 16 | 480878287553664000 |
| 17 | 22629566473113600000 |
| 18 | 833522365093017600000 |
[1,1,8,45,504,5040,86400,1247400,28828800, 544864320,15850598400,370507737600,12996271411200, 362038989312000,14867734494412800, 480878287553664000,22629566473113600000, 833522365093017600000] |