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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 18 |
| 3 | 1890 |
| 4 | 22680 |
| 5 | 1247400 |
| 6 | 157172400 |
| 7 | 6129723600 |
| 8 | 81729648000 |
| 9 | 127932046704000 |
| 10 | 1646485441080480000 |
| 11 | 37869165144851040000 |
| 12 | 62372742591519360000 |
| 13 | 9304453876089900528000000 |
| 14 | 5075156659685400288000000 |
| 15 | 4459030689216262044805920000000 |
[1,3,18,1890,22680,1247400,157172400,6129723600, 81729648000,127932046704000,1646485441080480000, 37869165144851040000,62372742591519360000, 9304453876089900528000000, 5075156659685400288000000, 4459030689216262044805920000000] |