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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 36 |
| 4 | 144 |
| 5 | 3600 |
| 6 | 14400 |
| 7 | 705600 |
| 8 | 2822400 |
| 9 | 228614400 |
| 10 | 914457600 |
| 11 | 110649369600 |
| 12 | 442597478400 |
| 13 | 74798973849600 |
| 14 | 299195895398400 |
| 15 | 67319076464640000 |
| 16 | 269276305858560000 |
| 17 | 77820852393123840000 |
| 18 | 311283409572495360000 |
| 19 | 112373310855670824960000 |
[1,1,4,36,144,3600,14400,705600,2822400,228614400, 914457600,110649369600,442597478400, 74798973849600,299195895398400,67319076464640000, 269276305858560000,77820852393123840000, 311283409572495360000,112373310855670824960000] |