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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 54 |
| 3 | 2240 |
| 4 | 294000 |
| 5 | 127534176 |
| 6 | 189691951680 |
| 7 | 994556567347200 |
| 8 | 18760374808177860000 |
| 9 | 1292781708803753625600000 |
| 10 | 329281303607781567523264143360 |
| 11 | 312866979311142515971112580848148480 |
| 12 | 1117139877664193310898467728367016525532160 |
[1,4,54,2240,294000,127534176,189691951680, 994556567347200,18760374808177860000, 1292781708803753625600000, 329281303607781567523264143360, 312866979311142515971112580848148480, 1117139877664193310898467728367016525532160] |