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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 6 |
| 3 | 16 |
| 4 | 280 |
| 5 | 1440 |
| 6 | 16352 |
| 7 | 111104 |
| 8 | 1072512 |
| 9 | 8281600 |
| 10 | 74866176 |
| 11 | 614068224 |
| 12 | 5409544192 |
| 13 | 45696688128 |
| 14 | 398896128000 |
| 15 | 3421054959616 |
| 16 | 29796895916032 |
| 17 | 257698176565248 |
| 18 | 2245655567138816 |
| 19 | 19520497243914240 |
| 20 | 170356407824547840 |
[0,6,16,280,1440,16352,111104,1072512,8281600, 74866176,614068224,5409544192,45696688128, 398896128000,3421054959616,29796895916032, 257698176565248,2245655567138816, 19520497243914240,170356407824547840] |