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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 2 |
| 3 | 6 |
| 4 | 16 |
| 5 | 120 |
| 6 | 360 |
| 7 | 5040 |
| 8 | 20160 |
| 9 | 241920 |
| 10 | 1814400 |
| 11 | 39916800 |
| 12 | 159667200 |
| 13 | 6227020800 |
| 14 | 43589145600 |
| 15 | 653837184000 |
| 16 | 8369115955200 |
| 17 | 355687428096000 |
| 18 | 2134124568576000 |
| 19 | 121645100408832000 |
| 20 | 810967336058880000 |
[2,2,6,16,120,360,5040,20160,241920,1814400, 39916800,159667200,6227020800,43589145600, 653837184000,8369115955200,355687428096000, 2134124568576000,121645100408832000, 810967336058880000] |