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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 75 |
| 4 | 56 |
| 5 | 6930 |
| 6 | 28512 |
| 7 | 2849847 |
| 8 | 972400 |
| 9 | 693870606 |
| 10 | 99936200 |
| 11 | 63488350926 |
| 12 | 475814969280 |
| 13 | 166184959669300 |
| 14 | 497980728000 |
| 15 | 78877488833249175 |
| 16 | 1489333512849120 |
| 17 | 1116126129558913110 |
| 18 | 1597083864660900000 |
| 19 | 4467282986266589095530 |
| 20 | 107279471180408841600 |
[1,1,4,75,56,6930,28512,2849847,972400,693870606, 99936200,63488350926,475814969280,166184959669300, 497980728000,78877488833249175,1489333512849120, 1116126129558913110,1597083864660900000, 4467282986266589095530,107279471180408841600] |