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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 108 |
| 4 | 6912 |
| 5 | 21600000 |
| 6 | 2332800000 |
| 7 | 1921161110400000 |
| 8 | 31476303632793600000 |
| 9 | 16727798278915463577600000 |
| 10 | 209097478486443294720000000000 |
[1,1,4,108,6912,21600000,2332800000, 1921161110400000,31476303632793600000, 16727798278915463577600000, 209097478486443294720000000000] |