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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 2 |
| 2 | 12 |
| 3 | 240 |
| 4 | 2520 |
| 5 | 31500 |
| 6 | 354816 |
| 7 | 4060056 |
| 8 | 45405360 |
| 9 | 505842480 |
| 10 | 5588869000 |
| 11 | 61464995592 |
| 12 | 672880545792 |
| 13 | 7340296254200 |
| 14 | 79824251379600 |
| 15 | 865788437880000 |
| 16 | 9368862119134560 |
| 17 | 101178055201047660 |
| 18 | 1090713358902182400 |
| 19 | 11739380070425284200 |
| 20 | 126171548138325690000 |
[0,2,12,240,2520,31500,354816,4060056,45405360, 505842480,5588869000,61464995592,672880545792, 7340296254200,79824251379600,865788437880000, 9368862119134560,101178055201047660, 1090713358902182400,11739380070425284200, 126171548138325690000] |