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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 36 |
| 5 | 240 |
| 6 | 1800 |
| 7 | 16800 |
| 8 | 191520 |
| 9 | 2328480 |
| 10 | 30240000 |
| 11 | 479001600 |
| 12 | 8083152000 |
| 13 | 142702560000 |
| 14 | 2731586457600 |
| 15 | 59056027430400 |
| 16 | 1320663933388800 |
| 17 | 30575780537702400 |
| 18 | 783699448602470400 |
| 19 | 21234672840116736000 |
| 20 | 591499300737945600000 |
[1,1,2,6,36,240,1800,16800,191520,2328480, 30240000,479001600,8083152000,142702560000, 2731586457600,59056027430400,1320663933388800, 30575780537702400,783699448602470400, 21234672840116736000,591499300737945600000] |