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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 18 |
| 2 | 468 |
| 3 | 15912 |
| 4 | 668304 |
| 5 | 33415200 |
| 6 | 1938081600 |
| 7 | 127913385600 |
| 8 | 9465590534400 |
| 9 | 776178423820800 |
| 10 | 69856058143872000 |
| 11 | 6845893698099456000 |
| 12 | 725664731998542336000 |
| 13 | 82725779447833826304000 |
[1,18,468,15912,668304,33415200,1938081600, 127913385600,9465590534400,776178423820800, 69856058143872000,6845893698099456000, 725664731998542336000,82725779447833826304000] |